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 2081 matching lines @@
       'browser/ui/views/apps/app_info_dialog/app_info_summary_panel.cc',
       'browser/ui/views/apps/app_info_dialog/app_info_summary_panel.h',
       'browser/ui/views/apps/app_window_native_widget_mac.h',
       'browser/ui/views/apps/app_window_native_widget_mac.mm',
       'browser/ui/views/apps/chrome_native_app_window_views.cc',
       'browser/ui/views/apps/chrome_native_app_window_views.h',
       'browser/ui/views/apps/chrome_native_app_window_views_mac.h',
       'browser/ui/views/apps/chrome_native_app_window_views_mac.mm',
       'browser/ui/views/apps/native_app_window_frame_view_mac.h',
       'browser/ui/views/apps/native_app_window_frame_view_mac.mm',
+      'browser/ui/views/new_back_shortcut_bubble.cc',
+      'browser/ui/views/new_back_shortcut_bubble.h',
       'browser/ui/views/bookmarks/bookmark_bubble_view.cc',
       'browser/ui/views/bookmarks/bookmark_bubble_view.h',
       'browser/ui/views/bookmarks/bookmark_editor_view.cc',
       'browser/ui/views/bookmarks/bookmark_editor_view.h',
       'browser/ui/views/browser_dialogs_views_mac.cc',
       'browser/ui/views/chrome_browser_main_extra_parts_views.cc',
       'browser/ui/views/chrome_browser_main_extra_parts_views.h',
       'browser/ui/views/chrome_constrained_window_views_client.cc',
       'browser/ui/views/chrome_constrained_window_views_client.h',
       'browser/ui/views/chrome_views_delegate.cc',
@@ skipping 1209 matching lines @@
           ],
           'sources': [
             '<@(chrome_browser_ui_non_mobile_sources)',
             '<@(chrome_browser_ui_omnibox_non_mobile_sources)',
           ],
         }],
       ],
     },
   ],
 }