[aw] Reuse WebContents PowerSaveBlocker in fullscreen.

android_webview/test/shell/assets/full_screen_video.js

 // Copyright (c) 2014 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.
 
 function goFullscreen(id) {
   var element = document.getElementById(id);
   if (element.webkitRequestFullScreen) {
     element.webkitRequestFullScreen();
   }
 }
 
 function playVideo() {
     document.getElementById('video').play();
 }
 
 addEventListener('DOMContentLoaded', function() {
-    document.addEventListener('webkitfullscreenchange', function() {
-        javaOnEnterFullscreen.notifyJava();
-    }, false);
-    document.getElementById('video').addEventListener('play', function() {
-        javaOnPlayObserver.notifyJava();
-    }, false);
     document.addEventListener('webkitfullscreenerror', function() {
         javaFullScreenErrorObserver.notifyJava();
     }, false);
 }, false);