Add heuristics to limit showing of new backspace UI bubble.

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 caef60c8165d7979b33b26ec310559740f3c014d..18792a1f6bc0e9d694f2000185b0b00f1d5ba7dc 100644
--- a/chrome/browser/ui/views/frame/browser_view.h
+++ b/chrome/browser/ui/views/frame/browser_view.h
@@ -13,6 +13,7 @@
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
+#include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "build/build_config.h"
 #include "chrome/browser/devtools/devtools_window.h"
@@ -287,7 +288,8 @@ class BrowserView : public BrowserWindow,
   bool ShouldHideUIForFullscreen() const override;
   bool IsFullscreen() const override;
   bool IsFullscreenBubbleVisible() const override;
-  void ShowNewBackShortcutBubble(bool forward) override;
+  void MaybeShowNewBackShortcutBubble(bool forward) override;
+  void HideNewBackShortcutBubble() override;
   LocationBar* GetLocationBar() const override;
   void SetFocusToLocationBar(bool select_all) override;
   void UpdateReloadStopState(bool is_loading, bool force) override;
@@ -669,6 +671,7 @@ class BrowserView : public BrowserWindow,
   std::unique_ptr<ExclusiveAccessBubbleViews> exclusive_access_bubble_;
 
   std::unique_ptr<NewBackShortcutBubble> new_back_shortcut_bubble_;
+  base::TimeTicks last_back_shortcut_press_time_;
 
 #if defined(OS_WIN)
   // Helper class to listen for completion of first page load.