Implement Android accessible hit testing using an IPC to the renderer process.

ui/accessibility/ax_enums.idl

 // Copyright 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.
 
 // These should be kept in sync with third_party/WebKit/public/web/WebAXEnums.h
 // until the Chromium and Blink trees are merged.
 [camel_case_enum_to_string=true] namespace ui {
   enum AXEvent {
     activedescendantchanged,
     alert,
     aria_attribute_changed,
     autocorrection_occured,
     blur,
     checked_state_changed,
     children_changed,
     focus,
     hide,
+    hover,
     invalid_status_changed,
     layout_complete,
     live_region_changed,
     load_complete,
     location_changed,
     menu_end,
     menu_list_item_selected,
     menu_list_value_changed,
     menu_popup_end,
     menu_popup_start,
@@ skipping 315 matching lines @@
     word_ends
   };
 
   [cpp_enum_prefix_override="ax"] enum AXTextDirection {
     text_direction_lr,
     text_direction_rl,
     text_direction_tb,
     text_direction_bt
   };
 };