Add always on top windows to the alt+tab list

ash/shell.h

 // Copyright (c) 2012 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 ASH_SHELL_H_
 #define ASH_SHELL_H_
 
 #include <utility>
 #include <vector>
 
@@ skipping 235 matching lines @@
   // Adds/removes observer.
   void AddShellObserver(ShellObserver* observer);
   void RemoveShellObserver(ShellObserver* observer);
 
 #if !defined(OS_MACOSX)
   AcceleratorController* accelerator_controller() {
     return accelerator_controller_.get();
   }
 #endif  // !defined(OS_MACOSX)
 
+  internal::ActivationController* activation_controller() {
+    return activation_controller_.get();
+  }
+
   aura::shared::CompoundEventFilter* env_filter() {
     return env_filter_;
   }
   internal::TooltipController* tooltip_controller() {
     return tooltip_controller_.get();
   }
   internal::EventRewriterEventFilter* event_rewriter_filter() {
     return event_rewriter_filter_.get();
   }
   internal::OverlayEventFilter* overlay_filter() {
@@ skipping 220 matching lines @@
 
   // Used by ash/shell.
   content::BrowserContext* browser_context_;
 
   DISALLOW_COPY_AND_ASSIGN(Shell);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELL_H_