Add a WebContentsImpl API to snapshot the accessibility tree.

content/content_tests.gypi

 # Copyright (c) 2013 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.
 
 {
   'variables': {
     'layouttest_support_content_sources': [
       'public/test/layouttest_support.h',
       'public/test/nested_message_pump_android.cc',
       'public/test/nested_message_pump_android.h',
@@ skipping 168 matching lines @@
       'browser/accessibility/accessibility_event_recorder.h',
       'browser/accessibility/accessibility_event_recorder_mac.mm',
       'browser/accessibility/accessibility_event_recorder_win.cc',
       'browser/accessibility/accessibility_ipc_error_browsertest.cc',
       'browser/accessibility/accessibility_mode_browsertest.cc',
       'browser/accessibility/cross_platform_accessibility_browsertest.cc',
       'browser/accessibility/dump_accessibility_browsertest_base.cc',
       'browser/accessibility/dump_accessibility_browsertest_base.h',
       'browser/accessibility/dump_accessibility_events_browsertest.cc',
       'browser/accessibility/dump_accessibility_tree_browsertest.cc',
+      'browser/accessibility/snapshot_ax_tree_browsertest.cc',
       'browser/accessibility/site_per_process_accessibility_browsertest.cc',
       'browser/battery_status/battery_monitor_impl_browsertest.cc',
       'browser/battery_status/battery_monitor_integration_browsertest.cc',
       'browser/bookmarklet_browsertest.cc',
       'browser/browser_side_navigation_browsertest.cc',
       'browser/child_process_launcher_browsertest.cc',
       'browser/child_process_security_policy_browsertest.cc',
       'browser/compositor/image_transport_factory_browsertest.cc',
       'browser/cross_site_transfer_browsertest.cc',
       'browser/database_browsertest.cc',
@@ skipping 1991 matching lines @@
                   'files': ['<(PRODUCT_DIR)/libnpapi_test_plugin.so'],
                 },
               ],
             }],
           ],
         },
       ],
     }],
   ],
 }