Introduce XGetImage() for GrabWindowSnapshot() in ChromeOS.

BUG=119492
TEST=manually done

Review URL: https://chromiumcodereview.appspot.com/10386124

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@137556 0039d316-1c4b-4281-b951-d872f2087c98
LRESULT RootWindowHostWin::OnCaptureChanged(UINT message,
                                            WPARAM w_param,
                                            LPARAM l_param) {
  if (has_capture_) {
    has_capture_ = false;
    root_window_->SetCapture(NULL);
  }
  return 0;
}

LRESULT RootWindowHostWin::OnCaptureChanged(UINT message,
                                            WPARAM w_param,
                                            LPARAM l_param) {
  if (has_capture_) {
    has_capture_ = false;
    root_window_->SetCapture(NULL);
  }
  return 0;
}
