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
void RootWindow::ShowCursor(bool show) {
  cursor_shown_ = show;
  host_->ShowCursor(show);
}

void RootWindow::ShowCursor(bool show) {
  cursor_shown_ = show;
  host_->ShowCursor(show);
}
