Provide the custom thumbnail for live preview of stacked panels

chrome/browser/ui/views/panels/taskbar_window_thumbnailer_win.h

Index: chrome/browser/ui/views/panels/taskbar_window_thumbnailer_win.h
diff --git a/chrome/browser/ui/views/panels/taskbar_window_thumbnailer_win.h b/chrome/browser/ui/views/panels/taskbar_window_thumbnailer_win.h
index 909d8b68371f07b1f2336942441da1b09ae42242..6d13b00daf9beeec817647643b609fab6be19957 100644
--- a/chrome/browser/ui/views/panels/taskbar_window_thumbnailer_win.h
+++ b/chrome/browser/ui/views/panels/taskbar_window_thumbnailer_win.h
@@ -11,19 +11,37 @@
 
 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,
@@ -33,8 +51,7 @@ class TaskbarWindowThumbnailerWin : public ui::HWNDMessageFilter {
                              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
@@ -42,7 +59,7 @@ class TaskbarWindowThumbnailerWin : public ui::HWNDMessageFilter {
   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);