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

Improved WebGL architecture

<!-- Please describe your changes on the following line: -->

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.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [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).

<!-- Either: -->
- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/17891)
<!-- Reviewable:end -->

1 files changed, 1 insertions, 7 deletions

diff --git a/components/script_traits/script_msg.rs b/components/script_traits/script_msg.rs
index 4fd8fca5c7f..156f85a2be7 100644
--- a/components/script_traits/script_msg.rs
+++ b/components/script_traits/script_msg.rs
@@ -12,7 +12,7 @@ use LoadData;
 use MozBrowserEvent;
 use WorkerGlobalScopeInit;
 use WorkerScriptLoadOrigin;
-use canvas_traits::CanvasMsg;
+use canvas_traits::canvas::CanvasMsg;
 use devtools_traits::{ScriptToDevtoolsControlMsg, WorkerId};
 use euclid::{Point2D, Size2D, TypedSize2D};
 use ipc_channel::ipc::IpcSender;
@@ -21,7 +21,6 @@ use msg::constellation_msg::{Key, KeyModifiers, KeyState};
 use net_traits::CoreResourceMsg;
 use net_traits::request::RequestInit;
 use net_traits::storage_thread::StorageType;
-use offscreen_gl_context::{GLContextAttributes, GLLimits};
 use servo_url::ImmutableOrigin;
 use servo_url::ServoUrl;
 use style_traits::CSSPixel;
@@ -78,11 +77,6 @@ pub enum ScriptMsg {
     /// Requests that a new 2D canvas thread be created. (This is done in the constellation because
     /// 2D canvases may use the GPU and we don't want to give untrusted content access to the GPU.)
     CreateCanvasPaintThread(Size2D<i32>, IpcSender<IpcSender<CanvasMsg>>),
-    /// Requests that a new WebGL thread be created. (This is done in the constellation because
-    /// WebGL uses the GPU and we don't want to give untrusted content access to the GPU.)
-    CreateWebGLPaintThread(Size2D<i32>,
-                           GLContextAttributes,
-                           IpcSender<Result<(IpcSender<CanvasMsg>, GLLimits), String>>),
     /// Notifies the constellation that this frame has received focus.
     Focus,
     /// Forward an event that was sent to the parent window.