Add WebGLContextAttributes support

This commit also:
* Allows to return non-rootable dictionaries from
Codegen.
* Merges the two context types in an enum type.

components/script/dom/webglrenderingcontext.rs

@@ -6,7 +6,7 @@ use canvas::webgl_paint_task::WebGLPaintTask;
 use canvas_traits::{CanvasMsg, CanvasWebGLMsg, CanvasCommonMsg};
 use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding;
 use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::{
-    WebGLRenderingContextMethods, WebGLRenderingContextConstants};
+    WebGLContextAttributes, WebGLRenderingContextMethods, WebGLRenderingContextConstants};
 use dom::bindings::global::{GlobalRef, GlobalField};
 use dom::bindings::js::{JS, JSRef, LayoutJS, Temporary};
 use dom::bindings::utils::{Reflector, reflect_dom_object};
@@ -23,6 +23,7 @@ use std::mem;
 use std::ptr;
 use std::sync::mpsc::{channel, Sender};
 use util::str::DOMString;
+use offscreen_gl_context::GLContextAttributes;
 
 #[dom_struct]
 pub struct WebGLRenderingContext {
@@ -33,9 +34,12 @@ pub struct WebGLRenderingContext {
 }
 
 impl WebGLRenderingContext {
-    fn new_inherited(global: GlobalRef, canvas: JSRef<HTMLCanvasElement>, size: Size2D<i32>)
+    fn new_inherited(global: GlobalRef,
+                     canvas: JSRef<HTMLCanvasElement>,
+                     size: Size2D<i32>,
+                     attrs: GLContextAttributes)
                      -> Result<WebGLRenderingContext, &'static str> {
-        let chan = try!(WebGLPaintTask::start(size));
+        let chan = try!(WebGLPaintTask::start(size, attrs));
 
         Ok(WebGLRenderingContext {
             reflector_: Reflector::new(),
@@ -45,9 +49,9 @@ impl WebGLRenderingContext {
         })
     }
 
-    pub fn new(global: GlobalRef, canvas: JSRef<HTMLCanvasElement>, size: Size2D<i32>)
+    pub fn new(global: GlobalRef, canvas: JSRef<HTMLCanvasElement>, size: Size2D<i32>, attrs: GLContextAttributes)
                -> Option<Temporary<WebGLRenderingContext>> {
-        match WebGLRenderingContext::new_inherited(global, canvas, size) {
+        match WebGLRenderingContext::new_inherited(global, canvas, size, attrs) {
             Ok(ctx) => Some(reflect_dom_object(box ctx, global,
                                                WebGLRenderingContextBinding::Wrap)),
             Err(msg) => {
@@ -69,6 +73,28 @@ impl Drop for WebGLRenderingContext {
 }
 
 impl<'a> WebGLRenderingContextMethods for JSRef<'a, WebGLRenderingContext> {
+    // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.2
+    fn GetContextAttributes(self) -> Option<WebGLContextAttributes> {
+        let (sender, receiver) = channel();
+
+        // If the send does not succeed, assume context lost
+        if let Err(_) = self.renderer.send(CanvasMsg::WebGL(CanvasWebGLMsg::GetContextAttributes(sender))) {
+            return None;
+        }
+        let attrs = receiver.recv().unwrap();
+
+        Some(WebGLContextAttributes {
+            alpha: attrs.alpha,
+            antialias: attrs.antialias,
+            depth: attrs.depth,
+            failIfMajorPerformanceCaveat: false,
+            preferLowPowerToHighPerformance: false,
+            premultipliedAlpha: attrs.premultiplied_alpha,
+            preserveDrawingBuffer: attrs.preserve_drawing_buffer,
+            stencil: attrs.stencil
+        })
+    }
+
     // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.9
     fn AttachShader(self, program: Option<JSRef<WebGLProgram>>, shader: Option<JSRef<WebGLShader>>) {
         let program_id = match program {