Auto merge of #17891 - MortimerGoro:webgl_move, r=glennw,emilio

Improved WebGL architecture

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Info about the big picture and the goals of the WebGL refactor in this thread: https://groups.google.com/forum/#!topic/mozilla.dev.servo/0WMGz60kKzQ

I tried to reduce this PR as much as possible as requested in the thread. I'll do separate PRs for other features (e.g.: Batch messages or use shared memory to improve frame times) or fixes.

Some tips to ease the review process:
- Most changes in DOM objects follow the same pattern (remove CanvasMsg wrapper and use the new sender method).
- WebGLCommands are the same ones as before (moved from webrender_api). So those lines are already reviewed.
- See WebGL traits in [components/canvas_traits/webgl.rs](https://github.com/servo/servo/pull/17891/files#diff-8701045d01505418701d0631d4d45562)
- See WebGLThread and WR External Image bridge in [components/canvas/webgl_thread.rs](https://github.com/servo/servo/pull/17891/files#diff-281554879f39a2a041f7a69d442a5d2e)
- The implementation submitted in this PR creates a single `WebGLThread` for all ScriptThread/Pipelines. See that in [components/canvas/webgl_mode/inprocess.rs](https://github.com/servo/servo/pull/17891/files#diff-250070c6c5a38c7f9fa0f5b3c101f68b)

The conformance tests will help to guarantee that we don't miss anything.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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1 files changed, 20 insertions, 5 deletions

diff --git a/components/layout/fragment.rs b/components/layout/fragment.rs
index 2510b185d1c..f4928262e99 100644
--- a/components/layout/fragment.rs
+++ b/components/layout/fragment.rs
@@ -8,7 +8,7 @@
 
 use ServoArc;
 use app_units::Au;
-use canvas_traits::CanvasMsg;
+use canvas_traits::canvas::CanvasMsg;
 use context::{LayoutContext, with_thread_local_font_context};
 use euclid::{Transform3D, Point2D, Vector2D, Radians, Rect, Size2D};
 use floats::ClearType;
@@ -30,7 +30,7 @@ use msg::constellation_msg::{BrowsingContextId, PipelineId};
 use net_traits::image::base::{Image, ImageMetadata};
 use net_traits::image_cache::{ImageOrMetadataAvailable, UsePlaceholder};
 use range::*;
-use script_layout_interface::HTMLCanvasData;
+use script_layout_interface::{HTMLCanvasData, HTMLCanvasDataSource};
 use script_layout_interface::SVGSVGData;
 use script_layout_interface::wrapper_traits::{PseudoElementType, ThreadSafeLayoutElement, ThreadSafeLayoutNode};
 use serde::ser::{Serialize, SerializeStruct, Serializer};
@@ -53,6 +53,7 @@ use style::values::{self, Either, Auto};
 use style::values::computed::{LengthOrPercentage, LengthOrPercentageOrAuto};
 use text;
 use text::TextRunScanner;
+use webrender_api;
 use wrapper::ThreadSafeLayoutNodeHelpers;
 
 // From gfxFontConstants.h in Firefox.
@@ -322,17 +323,31 @@ impl InlineAbsoluteFragmentInfo {
 }
 
 #[derive(Clone)]
+pub enum CanvasFragmentSource {
+    WebGL(webrender_api::ImageKey),
+    Image(Option<Arc<Mutex<IpcSender<CanvasMsg>>>>)
+}
+
+#[derive(Clone)]
 pub struct CanvasFragmentInfo {
-    pub ipc_renderer: Option<Arc<Mutex<IpcSender<CanvasMsg>>>>,
+    pub source: CanvasFragmentSource,
     pub dom_width: Au,
     pub dom_height: Au,
 }
 
 impl CanvasFragmentInfo {
     pub fn new(data: HTMLCanvasData) -> CanvasFragmentInfo {
+        let source = match data.source {
+            HTMLCanvasDataSource::WebGL(texture_id) => {
+                CanvasFragmentSource::WebGL(texture_id)
+            },
+            HTMLCanvasDataSource::Image(ipc_sender) => {
+                CanvasFragmentSource::Image(ipc_sender.map(|renderer| Arc::new(Mutex::new(renderer))))
+            }
+        };
+
         CanvasFragmentInfo {
-            ipc_renderer: data.ipc_renderer
-                              .map(|renderer| Arc::new(Mutex::new(renderer))),
+            source: source,
             dom_width: Au::from_px(data.width as i32),
             dom_height: Au::from_px(data.height as i32),
         }