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}
jint GetNativeInstanceCount(JNIEnv* env, const JavaParamRef<jclass>&) {
  return base::subtle::NoBarrier_Load(&g_instance_count);
}

jint GetNativeInstanceCount(JNIEnv* env, const JavaParamRef<jclass>&) {
  return base::subtle::NoBarrier_Load(&g_instance_count);
}
