Revert "compositor: Unify the cross process and in-process API (#36443)" (#36533)

This reverts commit 4c55104b36c7b858a117a6dd90a5dc21b74324d1.

This commit introduced an issue where messages from script to the
compositor no longer woke up the embedder. There is a larger issue
here, but this change exacerbated it.

Fixes #36528.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

8 files changed, 215 insertions, 95 deletions

diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
index cdbaf4bbffb..f4ecd82cbc1 100644
--- a/components/compositing/compositor.rs
+++ b/components/compositing/compositor.rs
@@ -19,7 +19,8 @@ use bitflags::bitflags;
 use compositing_traits::display_list::{CompositorDisplayListInfo, HitTestInfo, ScrollTree};
 use compositing_traits::rendering_context::RenderingContext;
 use compositing_traits::{
-    CompositionPipeline, CompositorMsg, ImageUpdate, RendererWebView, SendableFrameTree,
+    CompositionPipeline, CompositorMsg, CompositorReceiver, CrossProcessCompositorMessage,
+    ImageUpdate, RendererWebView, SendableFrameTree,
 };
 use constellation_traits::{AnimationTickType, EmbedderToConstellationMessage, PaintMetricEvent};
 use crossbeam_channel::Sender;
@@ -30,7 +31,7 @@ use embedder_traits::{
 };
 use euclid::{Point2D, Rect, Scale, Size2D, Transform3D};
 use fnv::FnvHashMap;
-use ipc_channel::ipc::{self, IpcReceiver, IpcSharedMemory};
+use ipc_channel::ipc::{self, IpcSharedMemory};
 use libc::c_void;
 use log::{debug, info, trace, warn};
 use pixels::{CorsStatus, Image, ImageFrame, PixelFormat};
@@ -89,7 +90,7 @@ pub struct ServoRenderer {
     shutdown_state: Rc<Cell<ShutdownState>>,
 
     /// The port on which we receive messages.
-    compositor_receiver: IpcReceiver<CompositorMsg>,
+    compositor_receiver: CompositorReceiver,
 
     /// The channel on which messages can be sent to the constellation.
     pub(crate) constellation_sender: Sender<EmbedderToConstellationMessage>,
@@ -466,8 +467,8 @@ impl IOCompositor {
             .global
             .borrow_mut()
             .compositor_receiver
-            .try_recv()
-            .is_ok()
+            .try_recv_compositor_msg()
+            .is_some()
         {}
 
         // Tell the profiler, memory profiler, and scrolling timer to shut down.
@@ -629,14 +630,33 @@ impl IOCompositor {
                 webview.dispatch_input_event(InputEvent::MouseMove(MouseMoveEvent { point }));
             },
 
-            CompositorMsg::SendInitialTransaction(pipeline) => {
+            CompositorMsg::CrossProcess(cross_proces_message) => {
+                self.handle_cross_process_message(cross_proces_message);
+            },
+        }
+    }
+
+    /// Accept messages from content processes that need to be relayed to the WebRender
+    /// instance in the parent process.
+    #[cfg_attr(
+        feature = "tracing",
+        tracing::instrument(skip_all, fields(servo_profiling = true), level = "trace")
+    )]
+    fn handle_cross_process_message(&mut self, msg: CrossProcessCompositorMessage) {
+        match msg {
+            CrossProcessCompositorMessage::SendInitialTransaction(pipeline) => {
                 let mut txn = Transaction::new();
                 txn.set_display_list(WebRenderEpoch(0), (pipeline, Default::default()));
                 self.generate_frame(&mut txn, RenderReasons::SCENE);
                 self.global.borrow_mut().send_transaction(txn);
             },
 
-            CompositorMsg::SendScrollNode(webview_id, pipeline_id, point, external_scroll_id) => {
+            CrossProcessCompositorMessage::SendScrollNode(
+                webview_id,
+                pipeline_id,
+                point,
+                external_scroll_id,
+            ) => {
                 let Some(webview) = self.webviews.get_mut(webview_id) else {
                     return;
                 };
@@ -670,7 +690,7 @@ impl IOCompositor {
                 self.global.borrow_mut().send_transaction(txn);
             },
 
-            CompositorMsg::SendDisplayList {
+            CrossProcessCompositorMessage::SendDisplayList {
                 webview_id,
                 display_list_descriptor,
                 display_list_receiver,
@@ -759,7 +779,7 @@ impl IOCompositor {
                 self.global.borrow_mut().send_transaction(transaction);
             },
 
-            CompositorMsg::HitTest(pipeline, point, flags, sender) => {
+            CrossProcessCompositorMessage::HitTest(pipeline, point, flags, sender) => {
                 // When a display list is sent to WebRender, it starts scene building in a
                 // separate thread and then that display list is available for hit testing.
                 // Without flushing scene building, any hit test we do might be done against
@@ -785,11 +805,11 @@ impl IOCompositor {
                 let _ = sender.send(result);
             },
 
-            CompositorMsg::GenerateImageKey(sender) => {
+            CrossProcessCompositorMessage::GenerateImageKey(sender) => {
                 let _ = sender.send(self.global.borrow().webrender_api.generate_image_key());
             },
 
-            CompositorMsg::UpdateImages(updates) => {
+            CrossProcessCompositorMessage::UpdateImages(updates) => {
                 let mut txn = Transaction::new();
                 for update in updates {
                     match update {
@@ -805,21 +825,26 @@ impl IOCompositor {
                 self.global.borrow_mut().send_transaction(txn);
             },
 
-            CompositorMsg::AddFont(font_key, data, index) => {
+            CrossProcessCompositorMessage::AddFont(font_key, data, index) => {
                 self.add_font(font_key, index, data);
             },
 
-            CompositorMsg::AddSystemFont(font_key, native_handle) => {
+            CrossProcessCompositorMessage::AddSystemFont(font_key, native_handle) => {
                 let mut transaction = Transaction::new();
                 transaction.add_native_font(font_key, native_handle);
                 self.global.borrow_mut().send_transaction(transaction);
             },
 
-            CompositorMsg::AddFontInstance(font_instance_key, font_key, size, flags) => {
+            CrossProcessCompositorMessage::AddFontInstance(
+                font_instance_key,
+                font_key,
+                size,
+                flags,
+            ) => {
                 self.add_font_instance(font_instance_key, font_key, size, flags);
             },
 
-            CompositorMsg::RemoveFonts(keys, instance_keys) => {
+            CrossProcessCompositorMessage::RemoveFonts(keys, instance_keys) => {
                 let mut transaction = Transaction::new();
 
                 for instance in instance_keys.into_iter() {
@@ -832,13 +857,13 @@ impl IOCompositor {
                 self.global.borrow_mut().send_transaction(transaction);
             },
 
-            CompositorMsg::AddImage(key, desc, data) => {
+            CrossProcessCompositorMessage::AddImage(key, desc, data) => {
                 let mut txn = Transaction::new();
                 txn.add_image(key, desc, data.into(), None);
                 self.global.borrow_mut().send_transaction(txn);
             },
 
-            CompositorMsg::GenerateFontKeys(
+            CrossProcessCompositorMessage::GenerateFontKeys(
                 number_of_font_keys,
                 number_of_font_instance_keys,
                 result_sender,
@@ -856,7 +881,7 @@ impl IOCompositor {
                     .collect();
                 let _ = result_sender.send((font_keys, font_instance_keys));
             },
-            CompositorMsg::GetClientWindowRect(webview_id, response_sender) => {
+            CrossProcessCompositorMessage::GetClientWindowRect(webview_id, response_sender) => {
                 let client_window_rect = self
                     .webviews
                     .get(webview_id)
@@ -866,7 +891,7 @@ impl IOCompositor {
                     warn!("Sending response to get client window failed ({error:?}).");
                 }
             },
-            CompositorMsg::GetScreenSize(webview_id, response_sender) => {
+            CrossProcessCompositorMessage::GetScreenSize(webview_id, response_sender) => {
                 let screen_size = self
                     .webviews
                     .get(webview_id)
@@ -876,7 +901,7 @@ impl IOCompositor {
                     warn!("Sending response to get screen size failed ({error:?}).");
                 }
             },
-            CompositorMsg::GetAvailableScreenSize(webview_id, response_sender) => {
+            CrossProcessCompositorMessage::GetAvailableScreenSize(webview_id, response_sender) => {
                 let available_screen_size = self
                     .webviews
                     .get(webview_id)
@@ -910,14 +935,16 @@ impl IOCompositor {
                 }
                 let _ = sender.send(());
             },
-            CompositorMsg::GenerateImageKey(sender) => {
+            CompositorMsg::CrossProcess(CrossProcessCompositorMessage::GenerateImageKey(
+                sender,
+            )) => {
                 let _ = sender.send(self.global.borrow().webrender_api.generate_image_key());
             },
-            CompositorMsg::GenerateFontKeys(
+            CompositorMsg::CrossProcess(CrossProcessCompositorMessage::GenerateFontKeys(
                 number_of_font_keys,
                 number_of_font_instance_keys,
                 result_sender,
-            ) => {
+            )) => {
                 let font_keys = (0..number_of_font_keys)
                     .map(|_| self.global.borrow().webrender_api.generate_font_key())
                     .collect();
@@ -931,17 +958,26 @@ impl IOCompositor {
                     .collect();
                 let _ = result_sender.send((font_keys, font_instance_keys));
             },
-            CompositorMsg::GetClientWindowRect(_, response_sender) => {
+            CompositorMsg::CrossProcess(CrossProcessCompositorMessage::GetClientWindowRect(
+                _,
+                response_sender,
+            )) => {
                 if let Err(error) = response_sender.send(Default::default()) {
                     warn!("Sending response to get client window failed ({error:?}).");
                 }
             },
-            CompositorMsg::GetScreenSize(_, response_sender) => {
+            CompositorMsg::CrossProcess(CrossProcessCompositorMessage::GetScreenSize(
+                _,
+                response_sender,
+            )) => {
                 if let Err(error) = response_sender.send(Default::default()) {
                     warn!("Sending response to get client window failed ({error:?}).");
                 }
             },
-            CompositorMsg::GetAvailableScreenSize(_, response_sender) => {
+            CompositorMsg::CrossProcess(CrossProcessCompositorMessage::GetAvailableScreenSize(
+                _,
+                response_sender,
+            )) => {
                 if let Err(error) = response_sender.send(Default::default()) {
                     warn!("Sending response to get client window failed ({error:?}).");
                 }
@@ -1564,7 +1600,12 @@ impl IOCompositor {
         // Check for new messages coming from the other threads in the system.
         let mut compositor_messages = vec![];
         let mut found_recomposite_msg = false;
-        while let Ok(msg) = self.global.borrow_mut().compositor_receiver.try_recv() {
+        while let Some(msg) = self
+            .global
+            .borrow_mut()
+            .compositor_receiver
+            .try_recv_compositor_msg()
+        {
             match msg {
                 CompositorMsg::NewWebRenderFrameReady(..) if found_recomposite_msg => {
                     // Only take one of duplicate NewWebRendeFrameReady messages, but do subtract
diff --git a/components/compositing/lib.rs b/components/compositing/lib.rs
index 996d9760a2d..2e09fd0b1ab 100644
--- a/components/compositing/lib.rs
+++ b/components/compositing/lib.rs
@@ -8,11 +8,10 @@ use std::cell::Cell;
 use std::rc::Rc;
 
 use compositing_traits::rendering_context::RenderingContext;
-use compositing_traits::{CompositorMsg, CompositorProxy};
+use compositing_traits::{CompositorProxy, CompositorReceiver};
 use constellation_traits::EmbedderToConstellationMessage;
 use crossbeam_channel::Sender;
 use embedder_traits::ShutdownState;
-use ipc_channel::ipc::IpcReceiver;
 use profile_traits::{mem, time};
 use webrender::RenderApi;
 use webrender_api::DocumentId;
@@ -33,7 +32,7 @@ pub struct InitialCompositorState {
     /// A channel to the compositor.
     pub sender: CompositorProxy,
     /// A port on which messages inbound to the compositor can be received.
-    pub receiver: IpcReceiver<CompositorMsg>,
+    pub receiver: CompositorReceiver,
     /// A channel to the constellation.
     pub constellation_chan: Sender<EmbedderToConstellationMessage>,
     /// A channel to the time profiler thread.
diff --git a/components/compositing/tracing.rs b/components/compositing/tracing.rs
index 0373d0f1d1a..907c931aebe 100644
--- a/components/compositing/tracing.rs
+++ b/components/compositing/tracing.rs
@@ -42,21 +42,7 @@ mod from_constellation {
                 Self::LoadComplete(..) => target!("LoadComplete"),
                 Self::WebDriverMouseButtonEvent(..) => target!("WebDriverMouseButtonEvent"),
                 Self::WebDriverMouseMoveEvent(..) => target!("WebDriverMouseMoveEvent"),
-                Self::SendInitialTransaction(..) => target!("SendInitialTransaction"),
-                Self::SendScrollNode(..) => target!("SendScrollNode"),
-                Self::SendDisplayList { .. } => target!("SendDisplayList"),
-                Self::HitTest(..) => target!("HitTest"),
-                Self::GenerateImageKey(..) => target!("GenerateImageKey"),
-                Self::AddImage(..) => target!("AddImage"),
-                Self::UpdateImages(..) => target!("UpdateImages"),
-                Self::GenerateFontKeys(..) => target!("GenerateFontKeys"),
-                Self::AddFont(..) => target!("AddFont"),
-                Self::AddSystemFont(..) => target!("AddSystemFont"),
-                Self::AddFontInstance(..) => target!("AddFontInstance"),
-                Self::RemoveFonts(..) => target!("RemoveFonts"),
-                Self::GetClientWindowRect(..) => target!("GetClientWindowRect"),
-                Self::GetScreenSize(..) => target!("GetScreenSize"),
-                Self::GetAvailableScreenSize(..) => target!("GetAvailableScreenSize"),
+                Self::CrossProcess(_) => target!("CrossProcess"),
             }
         }
     }
diff --git a/components/constellation/pipeline.rs b/components/constellation/pipeline.rs
index 58b5b1c58dc..b6e546acd48 100644
--- a/components/constellation/pipeline.rs
+++ b/components/constellation/pipeline.rs
@@ -291,7 +291,8 @@ impl Pipeline {
                     webrender_document: state.webrender_document,
                     cross_process_compositor_api: state
                         .compositor_proxy
-                        .cross_process_compositor_api(),
+                        .cross_process_compositor_api
+                        .clone(),
                     webgl_chan: state.webgl_chan,
                     webxr_registry: state.webxr_registry,
                     player_context: state.player_context,
diff --git a/components/script/dom/screen.rs b/components/script/dom/screen.rs
index 061b2da3eca..4d76b20d626 100644
--- a/components/script/dom/screen.rs
+++ b/components/script/dom/screen.rs
@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
-use compositing_traits::CompositorMsg;
+use compositing_traits::CrossProcessCompositorMessage;
 use dom_struct::dom_struct;
 use euclid::Size2D;
 use profile_traits::ipc;
@@ -41,7 +41,7 @@ impl Screen {
         self.window
             .compositor_api()
             .sender()
-            .send(CompositorMsg::GetScreenSize(
+            .send(CrossProcessCompositorMessage::GetScreenSize(
                 self.window.webview_id(),
                 sender,
             ))
@@ -57,7 +57,7 @@ impl Screen {
         self.window
             .compositor_api()
             .sender()
-            .send(CompositorMsg::GetAvailableScreenSize(
+            .send(CrossProcessCompositorMessage::GetAvailableScreenSize(
                 self.window.webview_id(),
                 sender,
             ))
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index 689e9689667..2b4f1e2bf55 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -1899,7 +1899,10 @@ impl Window {
         let (sender, receiver) =
             ProfiledIpc::channel::<DeviceIndependentIntRect>(timer_profile_chan).unwrap();
         let _ = self.compositor_api.sender().send(
-            compositing_traits::CompositorMsg::GetClientWindowRect(self.webview_id(), sender),
+            compositing_traits::CrossProcessCompositorMessage::GetClientWindowRect(
+                self.webview_id(),
+                sender,
+            ),
         );
         let rect = receiver.recv().unwrap_or_default();
         (
diff --git a/components/servo/lib.rs b/components/servo/lib.rs
index 642cff60cb0..68008775c42 100644
--- a/components/servo/lib.rs
+++ b/components/servo/lib.rs
@@ -48,8 +48,8 @@ pub use compositing_traits::rendering_context::{
     OffscreenRenderingContext, RenderingContext, SoftwareRenderingContext, WindowRenderingContext,
 };
 use compositing_traits::{
-    CompositorMsg, CompositorProxy, WebrenderExternalImageHandlers, WebrenderExternalImageRegistry,
-    WebrenderImageHandlerType,
+    CompositorMsg, CompositorProxy, CompositorReceiver, CrossProcessCompositorApi,
+    WebrenderExternalImageHandlers, WebrenderExternalImageRegistry, WebrenderImageHandlerType,
 };
 #[cfg(all(
     not(target_os = "windows"),
@@ -82,6 +82,7 @@ use gaol::sandbox::{ChildSandbox, ChildSandboxMethods};
 pub use gleam::gl;
 use gleam::gl::RENDERER;
 use ipc_channel::ipc::{self, IpcSender};
+use ipc_channel::router::ROUTER;
 pub use keyboard_types::*;
 use log::{Log, Metadata, Record, debug, warn};
 use media::{GlApi, NativeDisplay, WindowGLContext};
@@ -297,6 +298,8 @@ impl Servo {
         // messages to client may need to pump a platform-specific event loop
         // to deliver the message.
         let event_loop_waker = embedder.create_event_loop_waker();
+        let (compositor_proxy, compositor_receiver) =
+            create_compositor_channel(event_loop_waker.clone());
         let (embedder_proxy, embedder_receiver) = create_embedder_channel(event_loop_waker.clone());
         let time_profiler_chan = profile_time::Profiler::create(
             &opts.time_profiling,
@@ -304,12 +307,6 @@ impl Servo {
         );
         let mem_profiler_chan = profile_mem::Profiler::create();
 
-        let (compositor_sender, compositor_receiver) = ipc::channel().expect("ipc channel failure");
-        let compositor_proxy = CompositorProxy {
-            sender: compositor_sender,
-            event_loop_waker: event_loop_waker.clone(),
-        };
-
         let devtools_sender = if pref!(devtools_server_enabled) {
             Some(devtools::start_server(
                 pref!(devtools_server_port) as u16,
@@ -993,6 +990,34 @@ fn create_embedder_channel(
     )
 }
 
+fn create_compositor_channel(
+    event_loop_waker: Box<dyn EventLoopWaker>,
+) -> (CompositorProxy, CompositorReceiver) {
+    let (sender, receiver) = unbounded();
+
+    let (compositor_ipc_sender, compositor_ipc_receiver) =
+        ipc::channel().expect("ipc channel failure");
+
+    let cross_process_compositor_api = CrossProcessCompositorApi(compositor_ipc_sender);
+    let compositor_proxy = CompositorProxy {
+        sender,
+        cross_process_compositor_api,
+        event_loop_waker,
+    };
+
+    let compositor_proxy_clone = compositor_proxy.clone();
+    ROUTER.add_typed_route(
+        compositor_ipc_receiver,
+        Box::new(move |message| {
+            compositor_proxy_clone.send(CompositorMsg::CrossProcess(
+                message.expect("Could not convert Compositor message"),
+            ));
+        }),
+    );
+
+    (compositor_proxy, CompositorReceiver { receiver })
+}
+
 #[allow(clippy::too_many_arguments)]
 fn create_constellation(
     config_dir: Option<PathBuf>,
@@ -1029,11 +1054,11 @@ fn create_constellation(
     );
 
     let system_font_service = Arc::new(
-        SystemFontService::spawn(compositor_proxy.cross_process_compositor_api()).to_proxy(),
+        SystemFontService::spawn(compositor_proxy.cross_process_compositor_api.clone()).to_proxy(),
     );
 
     let (canvas_create_sender, canvas_ipc_sender) = CanvasPaintThread::start(
-        compositor_proxy.cross_process_compositor_api(),
+        compositor_proxy.cross_process_compositor_api.clone(),
         system_font_service.clone(),
         public_resource_threads.clone(),
     );
diff --git a/components/shared/compositing/lib.rs b/components/shared/compositing/lib.rs
index b598dc1277b..acc14e3de29 100644
--- a/components/shared/compositing/lib.rs
+++ b/components/shared/compositing/lib.rs
@@ -7,6 +7,7 @@
 use std::fmt::{Debug, Error, Formatter};
 
 use base::id::{PipelineId, WebViewId};
+use crossbeam_channel::{Receiver, Sender};
 use embedder_traits::{
     AnimationState, EventLoopWaker, MouseButton, MouseButtonAction, TouchEventResult,
 };
@@ -21,6 +22,7 @@ use webrender_api::DocumentId;
 pub mod display_list;
 pub mod rendering_context;
 
+use core::fmt;
 use std::collections::HashMap;
 use std::sync::{Arc, Mutex};
 
@@ -41,7 +43,11 @@ use webrender_api::{
 /// Sends messages to the compositor.
 #[derive(Clone)]
 pub struct CompositorProxy {
-    pub sender: IpcSender<CompositorMsg>,
+    pub sender: Sender<CompositorMsg>,
+    /// Access to [`Self::sender`] that is possible to send across an IPC
+    /// channel. These messages are routed via the router thread to
+    /// [`Self::sender`].
+    pub cross_process_compositor_api: CrossProcessCompositorApi,
     pub event_loop_waker: Box<dyn EventLoopWaker>,
 }
 
@@ -52,14 +58,24 @@ impl CompositorProxy {
         }
         self.event_loop_waker.wake();
     }
+}
+
+/// The port that the compositor receives messages on.
+pub struct CompositorReceiver {
+    pub receiver: Receiver<CompositorMsg>,
+}
 
-    pub fn cross_process_compositor_api(&self) -> CrossProcessCompositorApi {
-        CrossProcessCompositorApi(self.sender.clone())
+impl CompositorReceiver {
+    pub fn try_recv_compositor_msg(&mut self) -> Option<CompositorMsg> {
+        self.receiver.try_recv().ok()
+    }
+    pub fn recv_compositor_msg(&mut self) -> CompositorMsg {
+        self.receiver.recv().unwrap()
     }
 }
 
 /// Messages from (or via) the constellation thread to the compositor.
-#[derive(Deserialize, IntoStaticStr, Serialize)]
+#[derive(IntoStaticStr)]
 pub enum CompositorMsg {
     /// Alerts the compositor that the given pipeline has changed whether it is running animations.
     ChangeRunningAnimationsState(WebViewId, PipelineId, AnimationState),
@@ -96,6 +112,32 @@ pub enum CompositorMsg {
     /// WebDriver mouse move event
     WebDriverMouseMoveEvent(WebViewId, f32, f32),
 
+    /// Messages forwarded to the compositor by the constellation from other crates. These
+    /// messages are mainly passed on from the compositor to WebRender.
+    CrossProcess(CrossProcessCompositorMessage),
+}
+
+pub struct SendableFrameTree {
+    pub pipeline: CompositionPipeline,
+    pub children: Vec<SendableFrameTree>,
+}
+
+/// The subset of the pipeline that is needed for layer composition.
+#[derive(Clone)]
+pub struct CompositionPipeline {
+    pub id: PipelineId,
+    pub webview_id: WebViewId,
+}
+
+impl Debug for CompositorMsg {
+    fn fmt(&self, formatter: &mut Formatter) -> Result<(), Error> {
+        let string: &'static str = self.into();
+        write!(formatter, "{string}")
+    }
+}
+
+#[derive(Deserialize, Serialize)]
+pub enum CrossProcessCompositorMessage {
     /// Inform WebRender of the existence of this pipeline.
     SendInitialTransaction(WebRenderPipelineId),
     /// Perform a scroll operation.
@@ -155,29 +197,31 @@ pub enum CompositorMsg {
     GetAvailableScreenSize(WebViewId, IpcSender<DeviceIndependentIntSize>),
 }
 
-impl Debug for CompositorMsg {
-    fn fmt(&self, formatter: &mut Formatter) -> Result<(), Error> {
-        let string: &'static str = self.into();
-        write!(formatter, "{string}")
+impl fmt::Debug for CrossProcessCompositorMessage {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::AddImage(..) => f.write_str("AddImage"),
+            Self::GenerateFontKeys(..) => f.write_str("GenerateFontKeys"),
+            Self::AddSystemFont(..) => f.write_str("AddSystemFont"),
+            Self::SendInitialTransaction(..) => f.write_str("SendInitialTransaction"),
+            Self::SendScrollNode(..) => f.write_str("SendScrollNode"),
+            Self::SendDisplayList { .. } => f.write_str("SendDisplayList"),
+            Self::HitTest(..) => f.write_str("HitTest"),
+            Self::GenerateImageKey(..) => f.write_str("GenerateImageKey"),
+            Self::UpdateImages(..) => f.write_str("UpdateImages"),
+            Self::RemoveFonts(..) => f.write_str("RemoveFonts"),
+            Self::AddFontInstance(..) => f.write_str("AddFontInstance"),
+            Self::AddFont(..) => f.write_str("AddFont"),
+            Self::GetClientWindowRect(..) => f.write_str("GetClientWindowRect"),
+            Self::GetScreenSize(..) => f.write_str("GetScreenSize"),
+            Self::GetAvailableScreenSize(..) => f.write_str("GetAvailableScreenSize"),
+        }
     }
 }
 
-#[derive(Deserialize, Serialize)]
-pub struct SendableFrameTree {
-    pub pipeline: CompositionPipeline,
-    pub children: Vec<SendableFrameTree>,
-}
-
-/// The subset of the pipeline that is needed for layer composition.
-#[derive(Clone, Deserialize, Serialize)]
-pub struct CompositionPipeline {
-    pub id: PipelineId,
-    pub webview_id: WebViewId,
-}
-
 /// A mechanism to send messages from ScriptThread to the parent process' WebRender instance.
 #[derive(Clone, Deserialize, Serialize)]
-pub struct CrossProcessCompositorApi(pub IpcSender<CompositorMsg>);
+pub struct CrossProcessCompositorApi(pub IpcSender<CrossProcessCompositorMessage>);
 
 impl CrossProcessCompositorApi {
     /// Create a new [`CrossProcessCompositorApi`] struct that does not have a listener on the other
@@ -188,13 +232,18 @@ impl CrossProcessCompositorApi {
     }
 
     /// Get the sender for this proxy.
-    pub fn sender(&self) -> &IpcSender<CompositorMsg> {
+    pub fn sender(&self) -> &IpcSender<CrossProcessCompositorMessage> {
         &self.0
     }
 
     /// Inform WebRender of the existence of this pipeline.
     pub fn send_initial_transaction(&self, pipeline: WebRenderPipelineId) {
-        if let Err(e) = self.0.send(CompositorMsg::SendInitialTransaction(pipeline)) {
+        if let Err(e) = self
+            .0
+            .send(CrossProcessCompositorMessage::SendInitialTransaction(
+                pipeline,
+            ))
+        {
             warn!("Error sending initial transaction: {}", e);
         }
     }
@@ -207,7 +256,7 @@ impl CrossProcessCompositorApi {
         point: LayoutPoint,
         scroll_id: ExternalScrollId,
     ) {
-        if let Err(e) = self.0.send(CompositorMsg::SendScrollNode(
+        if let Err(e) = self.0.send(CrossProcessCompositorMessage::SendScrollNode(
             webview_id,
             pipeline_id,
             point,
@@ -226,7 +275,7 @@ impl CrossProcessCompositorApi {
     ) {
         let (display_list_data, display_list_descriptor) = list.into_data();
         let (display_list_sender, display_list_receiver) = ipc::bytes_channel().unwrap();
-        if let Err(e) = self.0.send(CompositorMsg::SendDisplayList {
+        if let Err(e) = self.0.send(CrossProcessCompositorMessage::SendDisplayList {
             webview_id,
             display_list_descriptor,
             display_list_receiver,
@@ -261,7 +310,9 @@ impl CrossProcessCompositorApi {
     ) -> Vec<CompositorHitTestResult> {
         let (sender, receiver) = ipc::channel().unwrap();
         self.0
-            .send(CompositorMsg::HitTest(pipeline, point, flags, sender))
+            .send(CrossProcessCompositorMessage::HitTest(
+                pipeline, point, flags, sender,
+            ))
             .expect("error sending hit test");
         receiver.recv().expect("error receiving hit test result")
     }
@@ -269,7 +320,9 @@ impl CrossProcessCompositorApi {
     /// Create a new image key. Blocks until the key is available.
     pub fn generate_image_key(&self) -> Option<ImageKey> {
         let (sender, receiver) = ipc::channel().unwrap();
-        self.0.send(CompositorMsg::GenerateImageKey(sender)).ok()?;
+        self.0
+            .send(CrossProcessCompositorMessage::GenerateImageKey(sender))
+            .ok()?;
         receiver.recv().ok()
     }
 
@@ -279,14 +332,19 @@ impl CrossProcessCompositorApi {
         descriptor: ImageDescriptor,
         data: SerializableImageData,
     ) {
-        if let Err(e) = self.0.send(CompositorMsg::AddImage(key, descriptor, data)) {
+        if let Err(e) = self.0.send(CrossProcessCompositorMessage::AddImage(
+            key, descriptor, data,
+        )) {
             warn!("Error sending image update: {}", e);
         }
     }
 
     /// Perform an image resource update operation.
     pub fn update_images(&self, updates: Vec<ImageUpdate>) {
-        if let Err(e) = self.0.send(CompositorMsg::UpdateImages(updates)) {
+        if let Err(e) = self
+            .0
+            .send(CrossProcessCompositorMessage::UpdateImages(updates))
+        {
             warn!("error sending image updates: {}", e);
         }
     }
@@ -299,7 +357,10 @@ impl CrossProcessCompositorApi {
         if keys.is_empty() && instance_keys.is_empty() {
             return;
         }
-        let _ = self.0.send(CompositorMsg::RemoveFonts(keys, instance_keys));
+        let _ = self.0.send(CrossProcessCompositorMessage::RemoveFonts(
+            keys,
+            instance_keys,
+        ));
     }
 
     pub fn add_font_instance(
@@ -309,7 +370,7 @@ impl CrossProcessCompositorApi {
         size: f32,
         flags: FontInstanceFlags,
     ) {
-        let _x = self.0.send(CompositorMsg::AddFontInstance(
+        let _x = self.0.send(CrossProcessCompositorMessage::AddFontInstance(
             font_instance_key,
             font_key,
             size,
@@ -318,11 +379,15 @@ impl CrossProcessCompositorApi {
     }
 
     pub fn add_font(&self, font_key: FontKey, data: Arc<IpcSharedMemory>, index: u32) {
-        let _ = self.0.send(CompositorMsg::AddFont(font_key, data, index));
+        let _ = self.0.send(CrossProcessCompositorMessage::AddFont(
+            font_key, data, index,
+        ));
     }
 
     pub fn add_system_font(&self, font_key: FontKey, handle: NativeFontHandle) {
-        let _ = self.0.send(CompositorMsg::AddSystemFont(font_key, handle));
+        let _ = self.0.send(CrossProcessCompositorMessage::AddSystemFont(
+            font_key, handle,
+        ));
     }
 
     pub fn fetch_font_keys(
@@ -331,7 +396,7 @@ impl CrossProcessCompositorApi {
         number_of_font_instance_keys: usize,
     ) -> (Vec<FontKey>, Vec<FontInstanceKey>) {
         let (sender, receiver) = ipc_channel::ipc::channel().expect("Could not create IPC channel");
-        let _ = self.0.send(CompositorMsg::GenerateFontKeys(
+        let _ = self.0.send(CrossProcessCompositorMessage::GenerateFontKeys(
             number_of_font_keys,
             number_of_font_instance_keys,
             sender,