Added notification when user presses backspace to use new shortcut.

chrome/browser/ui/views/frame/browser_view.h

Index: chrome/browser/ui/views/frame/browser_view.h
diff --git a/chrome/browser/ui/views/frame/browser_view.h b/chrome/browser/ui/views/frame/browser_view.h
index be01656f904ad23f2e6a3dff565dcf40cf3c34c9..6354e3a0a208ec2e02feb2c7ef499dd24895febd 100644
--- a/chrome/browser/ui/views/frame/browser_view.h
+++ b/chrome/browser/ui/views/frame/browser_view.h
@@ -53,6 +53,7 @@ class DownloadShelfView;
 class ExclusiveAccessBubbleViews;
 class InfoBarContainerView;
 class LocationBarView;
+class NewBackShortcutBubble;
 class StatusBubbleViews;
 class TabStrip;
 class ToolbarView;
@@ -289,6 +290,7 @@ class BrowserView : public BrowserWindow,
   bool ShouldHideUIForFullscreen() const override;
   bool IsFullscreen() const override;
   bool IsFullscreenBubbleVisible() const override;
+  void ShowNewBackShortcutBubble(bool forward) override;
   LocationBar* GetLocationBar() const override;
   void SetFocusToLocationBar(bool select_all) override;
   void UpdateReloadStopState(bool is_loading, bool force) override;
@@ -668,6 +670,8 @@ class BrowserView : public BrowserWindow,
 
   std::unique_ptr<ExclusiveAccessBubbleViews> exclusive_access_bubble_;
 
+  std::unique_ptr<NewBackShortcutBubble> new_back_shortcut_bubble_;
+
 #if defined(OS_WIN)
   // Helper class to listen for completion of first page load.
   std::unique_ptr<LoadCompleteListener> load_complete_listener_;