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..1ed23e072ad754b401f77e99acc7a418e4a6da10 100644
--- a/chrome/browser/ui/views/frame/browser_view.h
+++ b/chrome/browser/ui/views/frame/browser_view.h
@@ -31,6 +31,7 @@
 #include "chrome/browser/ui/views/frame/immersive_mode_controller.h"
 #include "chrome/browser/ui/views/frame/web_contents_close_handler.h"
 #include "chrome/browser/ui/views/load_complete_listener.h"
+#include "chrome/browser/ui/views/new_back_shortcut_bubble.h"

[Peter Kasting, 2016/05/24 23:35:08]

Nit: I think you can just forward-declare the type in this header and then
#include this in the .cc file.

[Matt Giuca, 2016/05/26 04:37:35]

Done.

 #include "chrome/common/features.h"
 #include "components/omnibox/browser/omnibox_popup_model_observer.h"
 #include "ui/base/accelerators/accelerator.h"
@@ -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_;