Add iterator support to FontFaceSet

Source/core/css/FontFaceSet.idl

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 14 matching lines @@
  * 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.
  */
 
 enum FontFaceSetLoadStatus { "loading", "loaded" };
 
 [
     ActiveDOMObject,
+    Iterable,
     SetWrapperReferenceFrom=document,
     NoInterfaceObject,
 ] interface FontFaceSet : EventTarget {
 
     attribute EventHandler onloading;
     attribute EventHandler onloadingdone;
     attribute EventHandler onloadingerror;
 
     [RaisesException] boolean check(DOMString font, optional DOMString text = " ");
     [CallWith=ScriptState] Promise load(DOMString font, optional DOMString text = " ");
     [MeasureAs=FontFaceSetReady, CallWith=ScriptState] Promise ready();
 
     [RaisesException] void add(FontFace fontFace);
     void clear();
     [RaisesException, ImplementedAs=remove] boolean delete(FontFace fontFace);
     void forEach(FontFaceSetForEachCallback callback, optional any thisArg);
     [RaisesException] boolean has(FontFace fontFace);
+    Iterator keys();
+    Iterator values();
+    Iterator entries();
 
     readonly attribute unsigned long size;
     readonly attribute FontFaceSetLoadStatus status;
 };