Ignores screenshot taking invocations if it's too close to the previous one.

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
@@ skipping 11 matching lines @@
 
   // 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 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_