Use standardized accelerator-to-shortcut code for new backspace shortcut UI.

chrome/browser/ui/views/new_back_shortcut_bubble.h

Index: chrome/browser/ui/views/new_back_shortcut_bubble.h
diff --git a/chrome/browser/ui/views/new_back_shortcut_bubble.h b/chrome/browser/ui/views/new_back_shortcut_bubble.h
index 4956eb7adbe194d699928e741f6ada19d68ec36a..4f8f9bb5c82fe562d4d915be410de231efe6ab7b 100644
--- a/chrome/browser/ui/views/new_back_shortcut_bubble.h
+++ b/chrome/browser/ui/views/new_back_shortcut_bubble.h
@@ -39,9 +39,9 @@ class NewBackShortcutBubble : public gfx::AnimationDelegate {
   // Returns whether the UI is currently visible.
   bool IsVisible() const;
 
-  // Ensures the UI is displaying the correct shortcut for forward/back based on
-  // |forward|, and resets the hide timer.
-  void UpdateContent(bool forward);
+  // Ensures the UI is displaying the correct shortcut for the given
+  // |command_id|, and resets the hide timer.
+  void UpdateContent(int command_id);
 
   // Fades out the UI immediately.
   void Hide();