Provide the custom thumbnail for live preview of stacked panels

chrome/browser/ui/views/panels/taskbar_window_thumbnailer_win.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_VIEWS_PANELS_TASKBAR_WINDOW_THUMBNAILER_WIN_H_
 #define CHROME_BROWSER_UI_VIEWS_PANELS_TASKBAR_WINDOW_THUMBNAILER_WIN_H_
 
 #include <vector>
 #include "base/memory/scoped_ptr.h"
 #include "ui/base/win/hwnd_subclass.h"
 
 class SkBitmap;
 
+class TaskbarWindowThumbnailerDelegateWin {
+ public:
+  // Returns the list of handles for all windows that are used to construct the
+  // thumbnail. If empty list is returned, the snapshot of current window
+  // is used.
+  virtual std::vector<HWND> GetSnapshotWindowHandles() const = 0;
+};
+
 // Provides the custom thumbnail and live preview for the window that appears
 // in the taskbar (Windows 7 and later).
 class TaskbarWindowThumbnailerWin : public ui::HWNDMessageFilter {
  public:
-  explicit TaskbarWindowThumbnailerWin(HWND hwnd);
+  TaskbarWindowThumbnailerWin(HWND hwnd,
+                              TaskbarWindowThumbnailerDelegateWin* delegate);
   virtual ~TaskbarWindowThumbnailerWin();
 
-  // Use the snapshots from all the windows in |snapshot_hwnds| to construct
-  // the thumbnail. If |snapshot_hwnds| is empty, use the snapshot of current
-  // window.
-  void Start(const std::vector<HWND>& snapshot_hwnds);
+  // Starts using the custom snapshot for live preview. The snapshot is only
+  // captured once when the system requests it, so the updates of the panels'
+  // content will not be automatically reflected in the thumbnail.
+  void Start();
+
+  // Stops providing the custom snapshot for live preview.
   void Stop();
 
+  // Captures the snapshot now instead of when the system requests it.
+  void CaptureSnapshot();
+
+  // Invalidates the snapshot such that a fresh copy can be obtained next time
+  // when the system requests it.
+  void InvalidateSnapshot();
+
  private:
   // Overridden from ui::HWNDMessageFilter:
   virtual bool FilterMessage(HWND hwnd,
                              UINT message,
                              WPARAM w_param,
                              LPARAM l_param,
                              LRESULT* l_result) OVERRIDE;
 
   // Message handlers.
-  bool OnDwmSendIconicThumbnail(
-      int width, int height, LRESULT* l_result);
+  bool OnDwmSendIconicThumbnail(int width, int height, LRESULT* l_result);
   bool OnDwmSendIconicLivePreviewBitmap(LRESULT* l_result);
 
   // Captures and returns the screenshot of the window. The caller is
   // responsible to release the returned SkBitmap instance.
   SkBitmap* CaptureWindowImage() const;
 
   HWND hwnd_;
-  std::vector<HWND> snapshot_hwnds_;
+  TaskbarWindowThumbnailerDelegateWin* delegate_;  // Weak, owns us.
   scoped_ptr<SkBitmap> capture_bitmap_;
 
   DISALLOW_COPY_AND_ASSIGN(TaskbarWindowThumbnailerWin);
 };
 
 #endif  // CHROME_BROWSER_UI_VIEWS_PANELS_TASKBAR_WINDOW_THUMBNAILER_WIN_H_