fonts: Simplify `FontContext` in two ways that affect the unit test (#33541)

This is done by no longer forwarding compositor-bound messages through
SystemFontService and making `FontContext` non-generic:

- Messages from the `FontContext` to the `Compositor` no longer need to be
  forwarded through the `SystemFontService`. Instead send these messages
  directly through the script IPC channel to the `Compositor`.

- Instead of adding a mock `SystemFontServiceProxy`, simply implement a
  mock `SystemFontService` on the other side of an IPC channel in the
  `font_context` unit test. This allows making `FontContext`
  non-generic, greatly simplifying the code. The extra complexity moves
  into the unit test.

These changes necessitate adding a new kind of `FontIdentifier`,
`FontIdentifier::Mock` due to the fact that local fonts have
platform-specific identifiers. This avoids having to pretend like the
system font service can have web fonts -- which was always a bit of a
hack.

These two changes are combined into one PR because they both require
extensive and similar chages in the font_context unit test which
dependended on the details of both of them.

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

1 files changed, 15 insertions, 19 deletions

diff --git a/components/shared/webrender/lib.rs b/components/shared/webrender/lib.rs
index 14f3d3d338a..accb73df316 100644
--- a/components/shared/webrender/lib.rs
+++ b/components/shared/webrender/lib.rs
@@ -192,24 +192,6 @@ pub trait WebRenderFontApi {
     ) -> FontInstanceKey;
     fn add_font(&self, data: Arc<IpcSharedMemory>, index: u32) -> FontKey;
     fn add_system_font(&self, handle: NativeFontHandle) -> FontKey;
-
-    /// Forward a `AddFont` message, sending it on to the compositor. This is used to get WebRender
-    /// [`FontKey`]s for web fonts in the per-layout `FontContext`.
-    fn forward_add_font_message(
-        &self,
-        data: Arc<IpcSharedMemory>,
-        font_index: u32,
-        result_sender: IpcSender<FontKey>,
-    );
-    /// Forward a `AddFontInstance` message, sending it on to the compositor. This is used to get
-    /// WebRender [`FontInstanceKey`]s for web fonts in the per-layout `FontContext`.
-    fn forward_add_font_instance_message(
-        &self,
-        font_key: FontKey,
-        size: f32,
-        flags: FontInstanceFlags,
-        result_receiver: IpcSender<FontInstanceKey>,
-    );
 }
 
 pub enum CanvasToCompositorMsg {
@@ -260,6 +242,8 @@ pub enum ScriptToCompositorMsg {
     UpdateImages(Vec<SerializedImageUpdate>),
     /// Remove the given font resources from our WebRender instance.
     RemoveFonts(Vec<FontKey>, Vec<FontInstanceKey>),
+    AddFontInstance(FontKey, f32, FontInstanceFlags, IpcSender<FontInstanceKey>),
+    AddFont(Arc<IpcSharedMemory>, u32, IpcSender<FontKey>),
 }
 
 /// A mechanism to send messages from networking to the WebRender instance.
@@ -294,11 +278,23 @@ impl WebRenderNetApi {
 pub struct WebRenderScriptApi(IpcSender<ScriptToCompositorMsg>);
 
 impl WebRenderScriptApi {
-    /// Create a new WebrenderIpcSender object that wraps the provided channel sender.
+    /// Create a new [`WebRenderScriptApi`] object that wraps the provided channel sender.
     pub fn new(sender: IpcSender<ScriptToCompositorMsg>) -> Self {
         Self(sender)
     }
 
+    /// Create a new [`WebRenderScriptApi`] object that does not have a listener on the
+    /// other end.
+    pub fn dummy() -> Self {
+        let (sender, _) = ipc::channel().unwrap();
+        Self::new(sender)
+    }
+
+    /// Get the sender for this proxy.
+    pub fn sender(&self) -> &IpcSender<ScriptToCompositorMsg> {
+        &self.0
+    }
+
     /// Inform WebRender of the existence of this pipeline.
     pub fn send_initial_transaction(&self, pipeline: WebRenderPipelineId) {
         if let Err(e) = self