Brushes up the code of screenshot filename.

ash/screenshot_delegate.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_SCREENSHOT_DELEGATE_H_
 #define ASH_SCREENSHOT_DELEGATE_H_
 
 namespace aura {
 class Window;
 }  // namespace aura
 
 namespace gfx {
 class Rect;
 }  // namespace gfx
 
 namespace ash {
 
 // Delegate for taking screenshots.
 class ScreenshotDelegate {
  public:
   virtual ~ScreenshotDelegate() {}
 
-  // The actual task of taking a screenshot for the given window.
-  // This method is called when the user wants to take a screenshot
-  // manually.
-  virtual void HandleTakeScreenshot(aura::Window* window) = 0;
+  // The actual task of taking a screenshot for each root window.
+  // This method is called when the user wants to take a screenshot manually.
+  virtual void HandleTakeScreenshotForAllRootWindows() = 0;
 
   // The actual task of taking a partial screenshot for the given
   // window.
   virtual void HandleTakePartialScreenshot(
       aura::Window* window, const gfx::Rect& rect) = 0;
 
   // Returns true if the system is ready to take screenshot.
   virtual bool CanTakeScreenshot() = 0;
 };
 }  // namespace ash
 
 #endif  // ASH_SCREENSHOT_DELEGATE_H_