Adding supported checks for WebGL

tools/dom/idl/dart/dart.idl

 // This file introduces / supplements and forces Dart declarations.
 
 [Supplemental,
  Constructor]
 interface AudioContext {};
 
 [Supplemental]
 interface Document {
   [Suppressed] DOMObject getCSSCanvasContext(in DOMString contextId, in DOMString name, in long width, in long height);
   CanvasRenderingContext getCSSCanvasContext(in DOMString contextId, in DOMString name, in long width, in long height);
@@ skipping 26 matching lines @@
 
 [Supplemental]
 interface Console {
   [Suppressed] void assert(in boolean condition);
   [CallWith=ScriptArguments|ScriptState] void assertCondition(boolean condition);
 };
 
 interface HTMLCanvasElement {
   [Suppressed] DOMString toDataURL([TreatNullAs=NullString, TreatUndefinedAs=NullString,Optional=DefaultIsUndefined] in DOMString type) raises(DOMException);
   [Custom] DOMString toDataURL([TreatNullAs=NullString, TreatUndefinedAs=NullString,Optional=DefaultIsUndefined] in DOMString type, [Optional] in float quality) raises(DOMException);
+
+  [Suppressed] DOMObject getContext([Optional=DefaultIsUndefined] in DOMString contextId);
+  [Custom] CanvasRenderingContext getContext([Optional=DefaultIsUndefined] in DOMString contextId, [Optional] in Dictionary attrs);

[sra1, 2013/01/29 02:17:34]

Drop the [Optional=DefaultIsUndefined]
The generator ignores that since in JS it forces passing missing arguments -
something required to not break existing code that is missing mandatory
arguments.

[blois, 2013/01/29 21:50:08]

Done.

 };
 
 [Supplemental]
 interface HTMLOptionsCollection {
   [Suppressed] void add([Optional] in HTMLOptionElement element, [Optional] in long before);
 };
 
 [Supplemental]
 interface HTMLSelectElement {
   [Suppressed] void add([Optional=DefaultIsUndefined] in HTMLElement element, [Optional=DefaultIsUndefined] in HTMLElement before);
@@ skipping 280 matching lines @@
   [Suppressed] boolean send(in DOMString data) raises(DOMException);
 
   [Custom] void send(DOMString data) raises(DOMException);
   [Custom] void send(Blob data) raises(DOMException);
   [Custom] void send(ArrayBuffer data) raises(DOMException);
   [Custom] void send(ArrayBufferView data) raises(DOMException);
 };
 
 [Suppressed]
 interface Entity {};