sync compositor: pass simple gfx types by const ref

See bug for reasoning

BUG=159273

Review URL: https://codereview.chromium.org/1417893006

Cr-Commit-Position: refs/heads/master@{#356653}
void SynchronousCompositorImpl::ReturnResources(
    const cc::CompositorFrameAck& frame_ack) {
  DCHECK(CalledOnValidThread());
  output_surface_->ReturnResources(frame_ack);
}

void SynchronousCompositorImpl::ReturnResources(
    const cc::CompositorFrameAck& frame_ack) {
  DCHECK(CalledOnValidThread());
  output_surface_->ReturnResources(frame_ack);
}
