Add use counters for lots of DOM APIs.

third_party/WebKit/Source/core/css/FontFaceSetLoadEvent.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 17 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 // https://dev.w3.org/csswg/css-font-loading/#fontfacesetloadevent
 
 // TODO(foolip): This interface should have a constructor and
 // [Exposed=Window,Worker], and thus not [NoInterfaceObject].
 [
     NoInterfaceObject,
 ] interface FontFaceSetLoadEvent : Event {
-    readonly attribute sequence<FontFace> fontfaces;
+    [MeasureAs=FontFaceSetAPI] readonly attribute sequence<FontFace> fontfaces;
 };