Added notification when user presses backspace to use new shortcut.

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
new file mode 100644
index 0000000000000000000000000000000000000000..282a2a0f6520084b120968da390d0e8af9178538
--- /dev/null
+++ b/chrome/browser/ui/views/new_back_shortcut_bubble.h
@@ -0,0 +1,68 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_UI_VIEWS_NEW_BACK_SHORTCUT_BUBBLE_H_
+#define CHROME_BROWSER_UI_VIEWS_NEW_BACK_SHORTCUT_BUBBLE_H_
+
+#include <memory>
+
+#include "base/compiler_specific.h"
+#include "base/macros.h"
+#include "base/timer/timer.h"
+#include "ui/gfx/animation/animation_delegate.h"
+
+class ExclusiveAccessBubbleViewsContext;
+class SubtleNotificationView;
+
+namespace gfx {
+class Animation;
+class Rect;
+class SlideAnimation;
+}
+
+namespace views {
+class View;
+class Widget;
+}
+
+// NewBackShortcutBubble shows a short-lived notification along the top of the
+// screen when the user presses the old Back/Forward shortcut, telling them how
+// to use the new shortcut. This will only be available for a few milestones to
+// let users adapt.
+// TODO(mgiuca): Remove this in M54 (https://crbug.com/610039).
+class NewBackShortcutBubble : public gfx::AnimationDelegate {
+ public:
+  NewBackShortcutBubble(ExclusiveAccessBubbleViewsContext* context,
+                        bool forward);
+  ~NewBackShortcutBubble() override;
+
+  void UpdateContent(bool forward);
+
+ private:
+  // gfx::AnimationDelegate:
+  void AnimationProgressed(const gfx::Animation* animation) override;
+  void AnimationEnded(const gfx::Animation* animation) override;
+
+  gfx::Rect GetPopupRect(bool ignore_animation_state) const;
+  void Hide();
+  void Show();
+  void OnTimerElapsed();
+
+  ExclusiveAccessBubbleViewsContext* const bubble_view_context_;
+
+  views::Widget* popup_;
+
+  // Animation controlling showing/hiding of the bubble.
+  std::unique_ptr<gfx::SlideAnimation> animation_;
+
+  // Timer before the bubble disappears.
+  base::OneShotTimer hide_timeout_;
+
+  // The contents of the popup.
+  SubtleNotificationView* view_;
+
+  DISALLOW_COPY_AND_ASSIGN(NewBackShortcutBubble);
+};
+
+#endif  // CHROME_BROWSER_UI_VIEWS_NEW_BACK_SHORTCUT_BUBBLE_H_