Added notification when user presses backspace to use new shortcut.

chrome/browser/ui/cocoa/browser_window_cocoa.mm

 // Copyright (c) 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.
 
 #include "chrome/browser/ui/cocoa/browser_window_cocoa.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/logging.h"
 #import "base/mac/sdk_forward_declarations.h"
@@ skipping 415 matching lines @@
 }
 
 bool BrowserWindowCocoa::IsFullscreen() const {
   return [controller_ isInAnyFullscreenMode];
 }
 
 bool BrowserWindowCocoa::IsFullscreenBubbleVisible() const {
   return false;  // Currently only called from toolkit-views website_settings.
 }
 
+void BrowserWindowCocoa::ShowNewBackShortcutBubble(bool forward) {
+  // TODO(mgiuca): Implement new back shortcut bubble Mac.
+  // https://crbug.com/610039.
+}
+
 LocationBar* BrowserWindowCocoa::GetLocationBar() const {
   return [controller_ locationBarBridge];
 }
 
 void BrowserWindowCocoa::SetFocusToLocationBar(bool select_all) {
   [controller_ focusLocationBar:select_all ? YES : NO];
 }
 
 void BrowserWindowCocoa::UpdateReloadStopState(bool is_loading, bool force) {
   [controller_ setIsLoading:is_loading force:force];
@@ skipping 382 matching lines @@
 ExclusiveAccessContext* BrowserWindowCocoa::GetExclusiveAccessContext() {
   return [controller_ exclusiveAccessController];
 }
 
 void BrowserWindowCocoa::ShowImeWarningBubble(
     const extensions::Extension* extension,
     const base::Callback<void(ImeWarningBubblePermissionStatus status)>&
         callback) {
   NOTREACHED() << "The IME warning bubble is unsupported on this platform.";
 }