Fix ImageData constructor infelicity.

Source/core/html/ImageData.idl

 /*
  * Copyright (C) 2008, 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 11 matching lines @@
  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#imagedata
 
 [
+    TypeChecking=Interface,
     Constructor(unsigned long width, unsigned long height),
-    Constructor(Uint8ClampedArray data, unsigned long width, [Default=Undefined] optional unsigned long height),
+    Constructor(Uint8ClampedArray data, unsigned long width, optional unsigned long height),
     Exposed=(Window,Worker),
     RaisesException=Constructor,
     WillBeGarbageCollected,
 ] interface ImageData {
     readonly attribute long width;
     readonly attribute long height;
 };