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 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, 1 insertions, 1 deletions

diff --git a/components/script/dom/webgluniformlocation.rs b/components/script/dom/webgluniformlocation.rs
index 228808303c4..47292adeb18 100644
--- a/components/script/dom/webgluniformlocation.rs
+++ b/components/script/dom/webgluniformlocation.rs
@@ -3,12 +3,12 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 // https://www.khronos.org/registry/webgl/specs/latest/1.0/webgl.idl
+use canvas_traits::webgl::WebGLProgramId;
 use dom::bindings::codegen::Bindings::WebGLUniformLocationBinding;
 use dom::bindings::js::Root;
 use dom::bindings::reflector::{Reflector, reflect_dom_object};
 use dom::window::Window;
 use dom_struct::dom_struct;
-use webrender_api::WebGLProgramId;
 
 #[dom_struct]
 pub struct WebGLUniformLocation {