Make tooltips toplevel windows on Linux

chrome/browser/ui/libgtk2ui/native_theme_gtk2.h

 // Copyright (c) 2013 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_LIBGTK2UI_NATIVE_THEME_GTK2_H_
 #define CHROME_BROWSER_UI_LIBGTK2UI_NATIVE_THEME_GTK2_H_
 
 #include "chrome/browser/ui/libgtk2ui/owned_widget_gtk2.h"
 #include "ui/native_theme/native_theme_base.h"
 
@@ skipping 29 matching lines @@
   // Implementation of GetSystemColor.
   GdkColor GetSystemGdkColor(ColorId color_id) const;
 
   // Returns styles associated with various widget types.
   GtkWidget* GetRealizedWindow() const;
   GtkStyle* GetWindowStyle() const;
   GtkStyle* GetEntryStyle() const;
   GtkStyle* GetLabelStyle() const;
   GtkStyle* GetButtonStyle() const;
   GtkStyle* GetTreeStyle() const;
+  GtkStyle* GetTooltipStyle() const;
   GtkStyle* GetMenuStyle() const;
   GtkStyle* GetMenuItemStyle() const;
 
   mutable GtkWidget* fake_window_;
+  mutable GtkWidget* fake_tooltip_;
   mutable OwnedWidgetGtk fake_entry_;
   mutable OwnedWidgetGtk fake_label_;
   mutable OwnedWidgetGtk fake_button_;
   mutable OwnedWidgetGtk fake_tree_;
 
   mutable OwnedWidgetGtk fake_menu_;
   mutable GtkWidget* fake_menu_item_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeThemeGtk2);
 };
 
 }  // namespace libgtk2ui
 
 #endif  // CHROME_BROWSER_UI_LIBGTK2UI_NATIVE_THEME_GTK2_H_