Use dictionaries for context creation attributes. Eliminate custom bindings.

Source/core/html/canvas/WebGLRenderingContext.h

Index: Source/core/html/canvas/WebGLRenderingContext.h
diff --git a/Source/core/html/canvas/WebGLRenderingContext.h b/Source/core/html/canvas/WebGLRenderingContext.h
index 31c81c3161150c09c7b4ba2001d58b7a9ec77558..1580cfe052d133e952f04ede522cdf9b407367e7 100644
--- a/Source/core/html/canvas/WebGLRenderingContext.h
+++ b/Source/core/html/canvas/WebGLRenderingContext.h
@@ -33,7 +33,7 @@ namespace blink {
 class WebGLRenderingContext final : public WebGLRenderingContextBase {
     DEFINE_WRAPPERTYPEINFO();
 public:
-    static PassOwnPtrWillBeRawPtr<WebGLRenderingContext> create(HTMLCanvasElement*, WebGLContextAttributes*);
+    static PassOwnPtrWillBeRawPtr<WebGLRenderingContext> create(HTMLCanvasElement*, const CanvasContextCreationAttributes&);
     static void forceNextWebGLContextCreationToFail();
     virtual ~WebGLRenderingContext();
 
@@ -44,7 +44,7 @@ public:
     virtual void trace(Visitor*) override;
 
 private:
-    WebGLRenderingContext(HTMLCanvasElement*, PassOwnPtr<blink::WebGraphicsContext3D>, WebGLContextAttributes*);
+    WebGLRenderingContext(HTMLCanvasElement*, PassOwnPtr<blink::WebGraphicsContext3D>, const WebGLContextAttributes&);
 
     // Enabled extension objects.
     RefPtrWillBeMember<ANGLEInstancedArrays> m_angleInstancedArrays;