Mac Overlays: Allow multiple overlays with sandwich strategy

cc/output/overlay_strategy_single_on_top.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_OUTPUT_OVERLAY_STRATEGY_SINGLE_ON_TOP_H_
 #define CC_OUTPUT_OVERLAY_STRATEGY_SINGLE_ON_TOP_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "cc/base/cc_export.h"
 #include "cc/output/overlay_candidate.h"
 #include "cc/output/overlay_processor.h"
 #include "cc/output/overlay_strategy_common.h"
 #include "cc/quads/render_pass.h"
 
 namespace cc {
 class StreamVideoDrawQuad;
 class TextureDrawQuad;
 
 class CC_EXPORT OverlayStrategySingleOnTop
     : public OverlayStrategyCommonDelegate {
  public:
   OverlayStrategySingleOnTop() {}
   ~OverlayStrategySingleOnTop() 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(OverlayStrategySingleOnTop);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_OVERLAY_STRATEGY_SINGLE_ON_TOP_H_