Implement initial support for nesting one ax tree in another.

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',
     '../crypto/crypto.gyp:crypto',
     '../google_apis/google_apis.gyp:google_apis',
     '../net/net.gyp:net',
@@ skipping 236 matching lines @@
     'browser/accessibility/browser_accessibility_manager_android.h',
     'browser/accessibility/browser_accessibility_manager_mac.h',
     'browser/accessibility/browser_accessibility_manager_mac.mm',
     'browser/accessibility/browser_accessibility_manager_win.cc',
     'browser/accessibility/browser_accessibility_manager_win.h',
     'browser/accessibility/browser_accessibility_state_impl.cc',
     'browser/accessibility/browser_accessibility_state_impl_win.cc',
     'browser/accessibility/browser_accessibility_state_impl.h',
     'browser/accessibility/browser_accessibility_win.cc',
     'browser/accessibility/browser_accessibility_win.h',
+    'browser/accessibility/frame_tree_accessibility.cc',
+    'browser/accessibility/frame_tree_accessibility.h',
     'browser/android/browser_jni_registrar.cc',
     'browser/android/browser_jni_registrar.h',
     'browser/android/browser_startup_controller.cc',
     'browser/android/browser_startup_controller.h',
     'browser/android/child_process_launcher_android.cc',
     'browser/android/child_process_launcher_android.h',
     'browser/android/content_settings.cc',
     'browser/android/content_settings.h',
     'browser/android/content_startup_flags.cc',
     'browser/android/content_startup_flags.h',
@@ skipping 1461 matching lines @@
         '../build/linux/system.gyp:dbus',
         '../dbus/dbus.gyp:dbus',
       ],
     }, {  # OS != "linux" or use_dbus==0
       'sources!': [
         'browser/geolocation/wifi_data_provider_linux.cc',
       ],
     }],
   ],
 }