Add use counters for lots of DOM APIs.

third_party/WebKit/Source/core/events/FocusEvent.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:
  * 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 10 matching lines @@
  * 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.
  */
 
 // https://w3c.github.io/uievents/#interface-FocusEvent
 
 [
     Constructor(DOMString type, optional FocusEventInit eventInitDict),
 ] interface FocusEvent : UIEvent {
-    readonly attribute EventTarget? relatedTarget;
+    [Measure] readonly attribute EventTarget? relatedTarget;
 };