Use dictionaries for context creation attributes. Eliminate custom bindings.

Source/core/html/HTMLCanvasElement.idl

Index: Source/core/html/HTMLCanvasElement.idl
diff --git a/Source/core/html/HTMLCanvasElement.idl b/Source/core/html/HTMLCanvasElement.idl
index 5f97987d6c470a235eaebfe8727debe77b9489e2..80d13f626a6cc3d9b1559c7522aeede277207d09 100644
--- a/Source/core/html/HTMLCanvasElement.idl
+++ b/Source/core/html/HTMLCanvasElement.idl
@@ -24,6 +24,8 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+typedef (CanvasRenderingContext2D or WebGLRenderingContext) RenderingContext;
+
 interface HTMLCanvasElement : HTMLElement {
 
     attribute long width;
@@ -31,6 +33,18 @@ interface HTMLCanvasElement : HTMLElement {
 
     [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.
+    //
+    // The PermissiveDictionaryConversion extended attribute is needed to allow the
+    // autogenerated code to match the behavior of the custom binding. Web IDL
+    // requires throwing TypeError if the incoming argument is not an object type
+    // (and is not undefined or null). The binding must ignore this.
+    //
+    // Also note: the only reason this must return type "any" is to allow the
+    // InspectorInstrumentation wrappers to be called for canvases. If that could be
+    // handled differently the return type could be changed to "RenderingContext?"
+    // and the [CallWith=ScriptState] extended attribute removed.
+    [CallWith=ScriptState] any getContext([Default=Undefined] optional DOMString contextId, [PermissiveDictionaryConversion] optional CanvasContextCreationAttributes attributes);
 };