Support overloaded constructors.

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 309 matching lines @@
   };
 
 [Supplemental]
 interface SQLResultSetRowList {
   // Change the return type to Dictionary so that rows are exposed in the Dart
   // API as a Maps, with the appropriate conversion in JavaScript.
   [Suppressed] DOMObject item(in unsigned long index);
   [Custom] Dictionary item(in unsigned long index);
 };
 
-[Supplemental, CustomConstructor, Constructor(in DOMString url)]
+[Supplemental]
 interface WebSocket {
   // Suppress the default since it has non-standard return type and add
   // overrides.
   [Suppressed] boolean send(in ArrayBuffer data) raises(DOMException);
   [Suppressed] boolean send(in ArrayBufferView data) raises(DOMException);
   [Suppressed] boolean send(in Blob data) raises(DOMException);
   [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 {};