Implement lifetime observer on RenderWidgetHostViewBase.

content/content_browser.gypi

 # Copyright (c) 2012 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.
 
 {
   'dependencies': [
     '../base/base.gyp:base_static',
     '../cc/cc.gyp:cc',
     '../cc/cc.gyp:cc_surfaces',
     '../components/filesystem/filesystem.gyp:filesystem_lib',
@@ skipping 1320 matching lines @@
       'browser/renderer_host/render_widget_host_delegate.h',
       'browser/renderer_host/render_widget_host_impl.cc',
       'browser/renderer_host/render_widget_host_impl.h',
       'browser/renderer_host/render_widget_host_input_event_router.cc',
       'browser/renderer_host/render_widget_host_input_event_router.h',
       'browser/renderer_host/render_widget_host_owner_delegate.h',
       'browser/renderer_host/render_widget_host_view_aura.cc',
       'browser/renderer_host/render_widget_host_view_aura.h',
       'browser/renderer_host/render_widget_host_view_base.cc',
       'browser/renderer_host/render_widget_host_view_base.h',
+      'browser/renderer_host/render_widget_host_view_base_observer.cc',
+      'browser/renderer_host/render_widget_host_view_base_observer.h',
       'browser/renderer_host/render_widget_host_view_mac.h',
       'browser/renderer_host/render_widget_host_view_mac.mm',
       'browser/renderer_host/render_widget_host_view_mac_dictionary_helper.h',
       'browser/renderer_host/render_widget_host_view_mac_dictionary_helper.mm',
       'browser/renderer_host/render_widget_host_view_mac_editcommand_helper.h',
       'browser/renderer_host/render_widget_host_view_mac_editcommand_helper.mm',
       'browser/renderer_host/render_widget_resize_helper_mac.cc',
       'browser/renderer_host/render_widget_resize_helper_mac.h',
       'browser/renderer_host/renderer_frame_manager.cc',
       'browser/renderer_host/renderer_frame_manager.h',
@@ skipping 844 matching lines @@
     ['enable_webvr==1 and OS=="android"', {
       'sources': [
         'browser/vr/android/cardboard/cardboard_vr_device.cc',
         'browser/vr/android/cardboard/cardboard_vr_device.h',
         'browser/vr/android/cardboard/cardboard_vr_device_provider.cc',
         'browser/vr/android/cardboard/cardboard_vr_device_provider.h',
       ],
     }],
   ],
 }