Enabling page visibility api in the chrome browser.

build/features_override.gypi

 # Copyright (c) 2011 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.
 
 # This file is only included in full-chromium builds, and overrides the
 # feature_defines variable in
 # third_party/WebKit/Source/WebKit/chromium/features.gypi.
 {
   'variables': {
     # WARNING: This list of strings completely replaces the list in
@@ skipping 28 matching lines @@
       'ENABLE_LEVELDB=1',
       'ENABLE_LINK_PREFETCH=1',
       'ENABLE_METER_TAG=1',
       'ENABLE_MEDIA_STATISTICS=1',
       'ENABLE_MEDIA_STREAM=1',
       'ENABLE_MHTML=1',
       'ENABLE_NOTIFICATIONS=1',
       'ENABLE_OFFLINE_WEB_APPLICATIONS=1',
       'ENABLE_OPENTYPE_SANITIZER=1',
       'ENABLE_ORIENTATION_EVENTS=0',
+      'ENABLE_PAGE_VISIBILITY_API=1',
       'ENABLE_PROGRESS_TAG=1',
       'ENABLE_QUOTA=1',
       'ENABLE_REQUEST_ANIMATION_FRAME=1',
       'ENABLE_RUBY=1',
       'ENABLE_SANDBOX=1',
       'ENABLE_SHARED_WORKERS=1',
       'ENABLE_SKIA_GPU=<(use_skia_gpu)',
       'ENABLE_SVG=<(enable_svg)',
       'ENABLE_SVG_ANIMATION=<(enable_svg)',
       'ENABLE_SVG_AS_IMAGE=<(enable_svg)',
@@ skipping 71 matching lines @@
     # require changes in gyp.
   },
 
 }
 
 # Local Variables:
 # tab-width:2
 # indent-tabs-mode:nil
 # End:
 # vim: set expandtab tabstop=2 shiftwidth=2: