cc: Ignore certain quads that would otherwise block overlays

cc/output/overlay_strategy_single_on_top.h

Index: cc/output/overlay_strategy_single_on_top.h
diff --git a/cc/output/overlay_strategy_single_on_top.h b/cc/output/overlay_strategy_single_on_top.h
index f92e10422b805cfb89d30509caee5b6d26bada38..5614bd84ff7df41a5f65ea3be702829a474afc42 100644
--- a/cc/output/overlay_strategy_single_on_top.h
+++ b/cc/output/overlay_strategy_single_on_top.h
@@ -29,6 +29,10 @@ class CC_EXPORT OverlayStrategySingleOnTop : public OverlayProcessor::Strategy {
   bool GetCandidateQuadInfo(const DrawQuad& draw_quad,
                             OverlayCandidate* quad_info);
 
+  // Returns true if |draw_quad| will block quads underneath from becoming an
+  // overlay.
+  bool DoesQuadBlockOverlay(const DrawQuad* draw_quad);
+
   bool GetTextureQuadInfo(const TextureDrawQuad& quad,
                           OverlayCandidate* quad_info);
   bool GetVideoQuadInfo(const StreamVideoDrawQuad& quad,