Use dictionaries for context creation attributes. Eliminate custom bindings.

Source/core/html/HTMLCanvasElement.idl

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+typedef (CanvasRenderingContext2D or WebGLRenderingContext) RenderingContext;
+
 interface HTMLCanvasElement : HTMLElement {
 
     attribute long width;
     attribute long height;
 
     [Custom, RaisesException] DOMString toDataURL([TreatUndefinedAs=NullString, Default=Undefined] optional DOMString? type);
 
-    // The custom binding is needed to handle context creation attributes.
-    [Custom] any getContext([Default=Undefined] optional DOMString contextId);
+    // Note: this differs deliberately from the specified Web IDL for this function:
+    //     RenderingContext? getContext(DOMString contextId, any... arguments);
+    // in order to eliminate the custom binding. It is functionally equivalent.
+    RenderingContext getContext([Default=Undefined] optional DOMString contextId, optional CanvasContextCreationAttributes attributes);

[bashi, 2014/12/12 00:35:24]

The return value is not nullable. Is this intentional too? If this is due to our
code generator's restriction (or bug), I'd happy to take a look.

[Ken Russell (switch to Gerrit), 2014/12/12 06:59:31]

No, that was an accident, and the code generator would have handled it correctly
-- but it turns out that in order to handle the InspectorInstrumentation's
wrapping of canvas contexts, I had to change the calling convention of this
method anyway, and add a little handwritten code in the epilogue. Please see the
next patch.

 };