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, 25 insertions, 4 deletions

diff --git a/components/script/dom/bindings/trace.rs b/components/script/dom/bindings/trace.rs
index 81017cd344e..4168fb4effa 100644
--- a/components/script/dom/bindings/trace.rs
+++ b/components/script/dom/bindings/trace.rs
@@ -30,8 +30,11 @@
 //! `JSTraceable` to a datatype.
 
 use app_units::Au;
-use canvas_traits::{CanvasGradientStop, LinearGradientStyle, RadialGradientStyle};
-use canvas_traits::{CompositionOrBlending, LineCapStyle, LineJoinStyle, RepetitionStyle};
+use canvas_traits::canvas::{CanvasGradientStop, LinearGradientStyle, RadialGradientStyle};
+use canvas_traits::canvas::{CompositionOrBlending, LineCapStyle, LineJoinStyle, RepetitionStyle};
+use canvas_traits::webgl::{WebGLBufferId, WebGLFramebufferId, WebGLProgramId, WebGLRenderbufferId};
+use canvas_traits::webgl::{WebGLChan, WebGLContextShareMode, WebGLError, WebGLPipeline, WebGLMsgSender};
+use canvas_traits::webgl::{WebGLReceiver, WebGLSender, WebGLShaderId, WebGLTextureId, WebGLVertexArrayId};
 use cssparser::RGBA;
 use devtools_traits::{CSSError, TimelineMarkerType, WorkerId};
 use dom::abstractworker::SharedRt;
@@ -105,8 +108,7 @@ use style::stylesheets::keyframes_rule::Keyframe;
 use style::values::specified::Length;
 use time::Duration;
 use uuid::Uuid;
-use webrender_api::{WebGLBufferId, WebGLError, WebGLFramebufferId, WebGLProgramId};
-use webrender_api::{WebGLRenderbufferId, WebGLShaderId, WebGLTextureId, WebGLVertexArrayId};
+use webrender_api::ImageKey;
 use webvr_traits::WebVRGamepadHand;
 
 /// A trait to allow tracing (only) DOM objects.
@@ -391,8 +393,13 @@ unsafe_no_jsmanaged_fields!(OpaqueStyleAndLayoutData);
 unsafe_no_jsmanaged_fields!(PathBuf);
 unsafe_no_jsmanaged_fields!(CSSErrorReporter);
 unsafe_no_jsmanaged_fields!(DrawAPaintImageResult);
+unsafe_no_jsmanaged_fields!(ImageKey);
 unsafe_no_jsmanaged_fields!(WebGLBufferId);
+unsafe_no_jsmanaged_fields!(WebGLChan);
+unsafe_no_jsmanaged_fields!(WebGLContextShareMode);
 unsafe_no_jsmanaged_fields!(WebGLFramebufferId);
+unsafe_no_jsmanaged_fields!(WebGLMsgSender);
+unsafe_no_jsmanaged_fields!(WebGLPipeline);
 unsafe_no_jsmanaged_fields!(WebGLProgramId);
 unsafe_no_jsmanaged_fields!(WebGLRenderbufferId);
 unsafe_no_jsmanaged_fields!(WebGLShaderId);
@@ -466,6 +473,20 @@ unsafe impl<T: Send> JSTraceable for Sender<T> {
     }
 }
 
+unsafe impl<T: Send> JSTraceable for WebGLReceiver<T> where T: for<'de> Deserialize<'de> + Serialize {
+    #[inline]
+    unsafe fn trace(&self, _: *mut JSTracer) {
+        // Do nothing
+    }
+}
+
+unsafe impl<T: Send> JSTraceable for WebGLSender<T> where T: for<'de> Deserialize<'de> + Serialize {
+    #[inline]
+    unsafe fn trace(&self, _: *mut JSTracer) {
+        // Do nothing
+    }
+}
+
 unsafe impl JSTraceable for Transform2D<f32> {
     #[inline]
     unsafe fn trace(&self, _trc: *mut JSTracer) {