Update context2d.arc to take optional anticlockwise parameter

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 120 matching lines @@
   [Suppressed, StrictTypeChecking, Custom] void getTexParameter();
 
   [Custom] any getUniform(in WebGLProgram program, in WebGLUniformLocation location) raises(DOMException);
   [Suppressed, StrictTypeChecking, Custom] void getUniform();
 
   [Custom] any getVertexAttrib(in unsigned long index, in unsigned long pname) raises(DOMException);
   [Suppressed, StrictTypeChecking, Custom] void getVertexAttrib();
 };
 
 [Supplemental]
+interface CanvasRenderingContext2D {
+    [Suppressed] any arc( float x,  float y,  float radius,  float startAngle,  float endAngle, boolean anticlockwise);
+    [Custom] void arc( float x,  float y,  float radius,  float startAngle,  float endAngle, [Optional] boolean anticlockwise);
+};
+
+[Supplemental]
 interface CSSStyleDeclaration {
   void setProperty(in DOMString propertyName, in DOMString value, [Optional] in DOMString priority);
   [DartName=_getPropertyValue] DOMString getPropertyValue(in DOMString propertyName);
 };
 
 [Supplemental,
   Constructor(in long length)]  // Add constructor signature.
 interface ArrayBuffer {
 };
 [Supplemental]
@@ skipping 107 matching lines @@
   [DartName=upperBound_] static IDBKeyRange upperBound(in any bound, [Optional] in boolean open) raises (IDBDatabaseException);
   [DartName=bound_] static IDBKeyRange bound(in any lower, in any upper, [Optional] in boolean lowerOpen, [Optional] in boolean upperOpen) raises (IDBDatabaseException);
 };
 
 interface EntrySync {
   // Native implementation is declared to return EntrySync.
   [Suppressed] DirectoryEntrySync getParent();
   EntrySync getParent();
 };
 
-
 [Supplemental,
   CustomConstructor,
   Constructor(in Array blobParts,
               [Optional] in DOMString type, [Optional] in DOMString endings)
   ]
 interface Blob {
 };
 
 [Supplemental,
   Constructor(float x, float y)
@@ skipping 71 matching lines @@
    [Conditional=BLOB, Custom] void send(in Blob data)
        raises(DOMException);
    [Custom] void send(in Document data)
        raises(DOMException);
    [Custom] void send([StrictTypeChecking] in DOMString data)
        raises(DOMException);
    [Custom] void send(in DOMFormData data)
        raises(DOMException);
 };
 
-
 [Suppressed]
 interface Entity {};