Rename the aura_shell namespace to ash

ash/screenshot_delegate.h

 // Copyright (c) 2011 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_SCREENSHOT_DELEGATE_H_
 #define ASH_SCREENSHOT_DELEGATE_H_
 #pragma once
 
-namespace aura_shell {
+namespace ash {
 
 // Delegate for taking screenshots.
 class ScreenshotDelegate {
  public:
   virtual ~ScreenshotDelegate() {}
 
   // The actual task of taking a screenshot.  This method is called
   // when the user wants to take a screenshot manually.
   virtual void HandleTakeScreenshot() = 0;
 };
-}  // namespace aura_shell
+}  // namespace ash
 
 #endif  // ASH_SCREENSHOT_DELEGATE_H_