Added notification when user presses backspace to use new shortcut.

chrome/chrome_browser_ui.gypi

 # Copyright 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.
 
 {
   'variables': {
     # There are two sections of sources:
     # * "Platform"-based sources (OS, toolkit, etc.)
     # * Feature/directory-based sources (e.g., history, printing)
 
@@ skipping 2113 matching lines @@
       'browser/ui/views/extensions/extension_install_dialog_view.cc',
       'browser/ui/views/extensions/extension_keybinding_registry_views.cc',
       'browser/ui/views/extensions/extension_keybinding_registry_views.h',
       'browser/ui/views/frame/native_widget_mac_frameless_nswindow.h',
       'browser/ui/views/frame/native_widget_mac_frameless_nswindow.mm',
       'browser/ui/views/location_bar/location_bar_bubble_delegate_view.cc',
       'browser/ui/views/location_bar/location_bar_bubble_delegate_view.h',
       'browser/ui/views/login_handler_views.cc',
       'browser/ui/views/login_view.cc',
       'browser/ui/views/login_view.h',
+      'browser/ui/views/new_back_shortcut_bubble.cc',
+      'browser/ui/views/new_back_shortcut_bubble.h',
       'browser/ui/views/new_task_manager_view.cc',
       'browser/ui/views/new_task_manager_view.h',
       'browser/ui/views/subtle_notification_view.cc',
       'browser/ui/views/subtle_notification_view.h',
       'browser/ui/views/sync/bubble_sync_promo_view.cc',
       'browser/ui/views/sync/bubble_sync_promo_view.h',
       'browser/ui/views/website_settings/chosen_object_view.cc',
       'browser/ui/views/website_settings/chosen_object_view.h',
       'browser/ui/views/website_settings/permission_selector_view.cc',
       'browser/ui/views/website_settings/permission_selector_view.h',
@@ skipping 1177 matching lines @@
           ],
           'sources': [
             '<@(chrome_browser_ui_non_mobile_sources)',
             '<@(chrome_browser_ui_omnibox_non_mobile_sources)',
           ],
         }],
       ],
     },
   ],
 }