Add an optional argument to HTMLCanvasElement.toDataURL.

lib/dom/idl/dart/dart.idl

Index: lib/dom/idl/dart/dart.idl
diff --git a/lib/dom/idl/dart/dart.idl b/lib/dom/idl/dart/dart.idl
index c1f1d63566f137d6a3ffaf637e955159d99788d4..afd3171b03bc65f56a0064136c8e3b7fe930c9d8 100644
--- a/lib/dom/idl/dart/dart.idl
+++ b/lib/dom/idl/dart/dart.idl
@@ -57,6 +57,12 @@ module html {
     [CallWith=ScriptArguments|CallStack] 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);
+
+  };
+
   [Supplemental]
   interface HTMLOptionsCollection {
     [Suppressed] void add([Optional] in HTMLOptionElement element, [Optional] in long before);