Enable cropping window capturing for Win7 when Aero is disabled.

webrtc/modules/desktop_capture/win/window_capture_utils.h

 /*
  *  Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include <windows.h>
 
 #include "webrtc/modules/desktop_capture/desktop_geometry.h"
 
 namespace webrtc {
 
 // Output the window rect, with the left/right/bottom frame border cropped if
 // the window is maximized. |cropped_rect| is the cropped rect relative to the
 // desktop. |original_rect| is the original rect returned from GetWindowRect.
 // Returns true if all API calls succeeded.
 bool GetCroppedWindowRect(HWND window,
                           DesktopRect* cropped_rect,
                           DesktopRect* original_rect);
 
+// Returns true if desktop composition (Aero) is enabled.
+bool IsAeroEnabled();
+
 }  // namespace webrtc