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, 12 insertions, 4 deletions

diff --git a/components/constellation/pipeline.rs b/components/constellation/pipeline.rs
index 92a5fb041ef..74ce33ff564 100644
--- a/components/constellation/pipeline.rs
+++ b/components/constellation/pipeline.rs
@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use bluetooth_traits::BluetoothRequest;
+use canvas_traits::webgl::WebGLPipeline;
 use compositing::CompositionPipeline;
 use compositing::CompositorProxy;
 use compositing::compositor_thread::Msg as CompositorMsg;
@@ -171,8 +172,12 @@ pub struct InitialPipelineState {
 
     /// Whether this pipeline is considered private.
     pub is_private: bool,
+
+    /// A channel to the webgl thread.
+    pub webgl_chan: WebGLPipeline,
+
     /// A channel to the webvr thread.
-    pub webvr_thread: Option<IpcSender<WebVRMsg>>,
+    pub webvr_chan: Option<IpcSender<WebVRMsg>>,
 }
 
 impl Pipeline {
@@ -270,7 +275,8 @@ impl Pipeline {
                     script_content_process_shutdown_port: script_content_process_shutdown_port,
                     webrender_api_sender: state.webrender_api_sender,
                     webrender_document: state.webrender_document,
-                    webvr_thread: state.webvr_thread,
+                    webgl_chan: state.webgl_chan,
+                    webvr_chan: state.webvr_chan,
                 };
 
                 // Spawn the child process.
@@ -470,7 +476,8 @@ pub struct UnprivilegedPipelineContent {
     script_content_process_shutdown_port: IpcReceiver<()>,
     webrender_api_sender: webrender_api::RenderApiSender,
     webrender_document: webrender_api::DocumentId,
-    webvr_thread: Option<IpcSender<WebVRMsg>>,
+    webgl_chan: WebGLPipeline,
+    webvr_chan: Option<IpcSender<WebVRMsg>>,
 }
 
 impl UnprivilegedPipelineContent {
@@ -499,7 +506,8 @@ impl UnprivilegedPipelineContent {
             window_size: self.window_size,
             pipeline_namespace_id: self.pipeline_namespace_id,
             content_process_shutdown_chan: self.script_content_process_shutdown_chan,
-            webvr_thread: self.webvr_thread,
+            webgl_chan: self.webgl_chan,
+            webvr_chan: self.webvr_chan,
         }, self.load_data.clone());
 
         LTF::create(self.id,