[IndexedDB] Added Observer UseCounter

third_party/WebKit/Source/modules/indexeddb/IDBObserver.idl

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // https://github.com/WICG/indexed-db-observers/issues/24
 
 callback IDBObserverCallback = void (IDBObserverChanges changes);
 
 [
    Exposed=(Window,Worker),
    CustomConstructor(IDBObserverCallback callback),
    RuntimeEnabled=IDBObserver
 ] interface IDBObserver {
-    [RaisesException] void observe(IDBDatabase db, IDBTransaction tx, IDBObserverInit options);
-    [RaisesException] void unobserve(IDBDatabase db);
+    [RaisesException, Measure] void observe(IDBDatabase db, IDBTransaction tx, IDBObserverInit options);
+    [RaisesException, Measure] void unobserve(IDBDatabase db);
 };