Added notification when user presses backspace to use new shortcut.

chrome/browser/ui/browser_window.h

Index: chrome/browser/ui/browser_window.h
diff --git a/chrome/browser/ui/browser_window.h b/chrome/browser/ui/browser_window.h
index 43837dd1013dc07308226ea54ae6d2868ad79aad..34e5e509b278477f87a49933a84dca42b7c9fa82 100644
--- a/chrome/browser/ui/browser_window.h
+++ b/chrome/browser/ui/browser_window.h
@@ -146,6 +146,10 @@ class BrowserWindow : public ui::BaseWindow {
   // Returns true if the fullscreen bubble is visible.
   virtual bool IsFullscreenBubbleVisible() const = 0;
 
+  // Shows a notice teaching the user the new shortcut for going Back or
+  // Forward.
+  virtual void ShowNewBackShortcutBubble(bool forward) = 0;
+
   // Returns the size of WebContents in the browser. This may be called before
   // the TabStripModel has an active tab.
   virtual gfx::Size GetContentsSize() const = 0;