First cut at Exit Fullscreen bubble on Linux.

chrome/browser/gtk/fullscreen_exit_bubble_gtk.h

+// Copyright (c) 2009 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_GTK_FULLSCREEN_EXIT_BUBBLE_GTK_H_
+#define CHROME_BROWSER_GTK_FULLSCREEN_EXIT_BUBBLE_GTK_H_
+
+#include <gtk/gtk.h>
+
+#include "base/timer.h"
+#include "chrome/common/owned_widget_gtk.h"
+
+typedef struct _GtkFloatingContainer GtkFloatingContainer;
+
+// FullscreenExitBubbleGTK is responsible for showing a bubble atop the screen
+// in fullscreen mode, telling users how to exit and providing a click target.
+class FullscreenExitBubbleGtk {
+ public:
+  // We place the bubble in |container|.
+  explicit FullscreenExitBubbleGtk(GtkFloatingContainer* container);
+  ~FullscreenExitBubbleGtk();
+
+  void InitWidgets();
+
+ private:
+  // Hide the exit bubble.
+  void Hide();
+
+  static void OnSetFloatingPosition(GtkFloatingContainer* floating_container,
+                                    GtkAllocation* allocation,
+                                    FullscreenExitBubbleGtk* bubble);
+
+  static void OnLinkClicked(GtkWidget* link,
+                            FullscreenExitBubbleGtk* bubble);
+
+  // A pointer to the floating container that is our parent.
+  GtkFloatingContainer* container_;
+
+  // The top widget of the exit bubble.
+  OwnedWidgetGtk alignment_;
+
+  // The timer that does the initial hiding of the exit bubble.
+  base::OneShotTimer<FullscreenExitBubbleGtk> initial_delay_;
+};
+
+#endif  // CHROME_BROWSER_GTK_FULLSCREEN_EXIT_BUBBLE_GTK_H_