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

chrome/browser/ui/ash/screenshot_taker.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 CHROME_BROWSER_UI_ASH_SCREENSHOT_TAKER_H_
 #define CHROME_BROWSER_UI_ASH_SCREENSHOT_TAKER_H_
 
 #include "ash/screenshot_delegate.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
+#include "base/time.h"
 #include "ui/compositor/layer.h"
 
 namespace aura {
 class Window;
 }  // namespace aura
 
 class ScreenshotTaker : public ash::ScreenshotDelegate {
  public:
   ScreenshotTaker();
   virtual ~ScreenshotTaker();
 
   // Overridden from ash::ScreenshotDelegate:
   virtual void HandleTakeScreenshot(aura::Window* window) OVERRIDE;
-  virtual void HandleTakePartialScreenshot(
-      aura::Window* window, const gfx::Rect& rect) OVERRIDE;
+  virtual void HandleTakePartialScreenshot(aura::Window* window,
+                                           const gfx::Rect& rect) OVERRIDE;
+  virtual bool CanTakeScreenshot() OVERRIDE;
 
  private:
   // Flashes the screen to provide visual feedback that a screenshot has
   // been taken.
   void DisplayVisualFeedback(const gfx::Rect& rect);
 
   // Closes the visual feedback layer.
   void CloseVisualFeedbackLayer();
 
+  // The timestamp when the screenshot task was issued last time.
+  base::Time last_screenshot_timestamp_;
+
+  // The flashing effect of the screen for the visual feedback when taking a
+  // screenshot.
   scoped_ptr<ui::Layer> visual_feedback_layer_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenshotTaker);
 };
 
 #endif  // CHROME_BROWSER_UI_ASH_SCREENSHOT_TAKER_H_