Implement overscroll support for the virtual keyboard.

ui/keyboard/keyboard.gyp

 # 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': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 43 matching lines @@
       'defines': [
         'KEYBOARD_IMPLEMENTATION',
       ],
       'sources': [
         'keyboard.cc',
         'keyboard.h',
         'keyboard_constants.cc',
         'keyboard_constants.h',
         'keyboard_controller.cc',
         'keyboard_controller.h',
-        'keyboard_controller_observer.h',
         'keyboard_controller_proxy.cc',
         'keyboard_controller_proxy.h',
         'keyboard_layout_manager.h',
         'keyboard_layout_manager.cc',
         'keyboard_export.h',
         'keyboard_switches.cc',
         'keyboard_switches.h',
         'keyboard_ui_controller.cc',
         'keyboard_ui_controller.h',
         'keyboard_ui_handler.cc',
@@ skipping 38 matching lines @@
         }],
         ['OS=="win" and win_use_allocator_shim==1', {
           'dependencies': [
             '<(DEPTH)/base/allocator/allocator.gyp:allocator',
           ],
         }],
       ],
     },
   ],
 }