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..fdf92de8f8122a9f6a5fe0acc66e4a7562e36c1d 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 (if
+  // |!forward|) or Forward (if |forward|).

[Peter Kasting, 2016/05/19 10:08:36]

Nit: I'd remove the parentheticals, the function of the arg is pretty clear
given the rest of this comment and they just make it read more awkwardly.

[Matt Giuca, 2016/05/23 04:22:56]

Done.

+  virtual void ShowBackspaceNewShortcutBubble(bool forward) = 0;

[Peter Kasting, 2016/05/19 10:08:36]

Nit: I would name this function, similar functions, the new file, etc.
"ShowNewBackShortcutBubble()", since this is about a bubble for a new "Go Back"
shortcut.  The name here reads a bit like backspace is a new shortcut, which
isn't right, and doesn't really flow as a sentence/phrase anyway.

[Matt Giuca, 2016/05/23 04:22:56]

Done.

+
   // 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;