Mac Overlays: Allow multiple overlays with sandwich strategy.

cc/output/overlay_strategy_sandwich.h

Index: cc/output/overlay_strategy_sandwich.h
diff --git a/cc/output/overlay_strategy_sandwich.h b/cc/output/overlay_strategy_sandwich.h
index c5c05e546cb2743d1fb29f328c67ae10f78de433..a1bd9d1bb24e7ea0200f6ab380eadb0992013c33 100644
--- a/cc/output/overlay_strategy_sandwich.h
+++ b/cc/output/overlay_strategy_sandwich.h
@@ -18,12 +18,12 @@ class CC_EXPORT OverlayStrategySandwich : public OverlayStrategyCommonDelegate {
   OverlayStrategySandwich() {}
   ~OverlayStrategySandwich() override;
 
-  bool TryOverlay(OverlayCandidateValidator* capability_checker,
-                  RenderPassList* render_passes_in_draw_order,
-                  OverlayCandidateList* candidate_list,
-                  const OverlayCandidate& candidate,
-                  QuadList::Iterator candidate_iterator,
-                  float device_scale_factor) override;
+  OverlayResult TryOverlay(OverlayCandidateValidator* capability_checker,
+                           RenderPassList* render_passes_in_draw_order,
+                           OverlayCandidateList* candidate_list,
+                           const OverlayCandidate& candidate,
+                           QuadList::Iterator* candidate_iterator,
+                           float device_scale_factor) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(OverlayStrategySandwich);