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::Init() {
  compositor()->SetScaleAndSize(GetDeviceScaleFactorFromMonitor(this),
                                host_->GetBounds().size());
  Window::Init(ui::LAYER_NOT_DRAWN);
  last_mouse_location_ =
      ui::ConvertPointToDIP(layer(), host_->QueryMouseLocation());
  compositor()->SetRootLayer(layer());
  SetBounds(
      ui::ConvertRectToDIP(layer(), gfx::Rect(host_->GetBounds().size())));
  Show();
  host_->SetRootWindow(this);
}

void RootWindow::Init() {
  compositor()->SetScaleAndSize(GetDeviceScaleFactorFromMonitor(this),
                                host_->GetBounds().size());
  Window::Init(ui::LAYER_NOT_DRAWN);
  last_mouse_location_ =
      ui::ConvertPointToDIP(layer(), host_->QueryMouseLocation());
  compositor()->SetRootLayer(layer());
  SetBounds(
      ui::ConvertRectToDIP(layer(), gfx::Rect(host_->GetBounds().size())));
  Show();
  host_->SetRootWindow(this);
}
