Add heuristics to limit showing of new backspace UI bubble.

chrome/browser/ui/cocoa/browser/exclusive_access_controller_views.h

Index: chrome/browser/ui/cocoa/browser/exclusive_access_controller_views.h
diff --git a/chrome/browser/ui/cocoa/browser/exclusive_access_controller_views.h b/chrome/browser/ui/cocoa/browser/exclusive_access_controller_views.h
index c705ed913975962c13ba055981ff91d3edc265c4..1ba1e7fb492acc0fcac79b65be0edc91ae64b601 100644
--- a/chrome/browser/ui/cocoa/browser/exclusive_access_controller_views.h
+++ b/chrome/browser/ui/cocoa/browser/exclusive_access_controller_views.h
@@ -14,6 +14,7 @@
 
 #import "base/mac/scoped_nsobject.h"
 #include "base/macros.h"
+#include "base/time/time.h"
 #include "chrome/browser/ui/exclusive_access/exclusive_access_context.h"
 #include "chrome/browser/ui/views/exclusive_access_bubble_views_context.h"
 #include "components/prefs/pref_change_registrar.h"
@@ -43,8 +44,9 @@ class ExclusiveAccessController : public ExclusiveAccessContext,
   // Shows the bubble once the NSWindow has received -windowDidEnterFullScreen:.
   void Show();
 
-  // Shows the new Back shortcut bubble.
-  void ShowNewBackShortcutBubble(bool forward);
+  // See comments on BrowserWindow::{MaybeShow,Hide}NewBackShortcutBubble().
+  void MaybeShowNewBackShortcutBubble(bool forward);
+  void HideNewBackShortcutBubble();
 
   // Closes any open bubble.
   void Destroy();
@@ -102,6 +104,7 @@ class ExclusiveAccessController : public ExclusiveAccessContext,
   // This class also manages the new Back shortcut bubble (which functions the
   // same way as ExclusiveAccessBubbleViews).
   std::unique_ptr<NewBackShortcutBubble> new_back_shortcut_bubble_;
+  base::TimeTicks last_back_shortcut_press_time_;
 
   // Used to keep track of the kShowFullscreenToolbar preference.
   PrefChangeRegistrar pref_registrar_;