Mac Overlays: Add sandwich strategy

cc/output/overlay_processor.h

Index: cc/output/overlay_processor.h
diff --git a/cc/output/overlay_processor.h b/cc/output/overlay_processor.h
index e37816c9565658c00778318d6c2c30d07f6e8f81..d18d6a0d581dc418a86276b466ba0e011866003a 100644
--- a/cc/output/overlay_processor.h
+++ b/cc/output/overlay_processor.h
@@ -17,6 +17,13 @@ class ResourceProvider;
 
 class CC_EXPORT OverlayProcessor {
  public:
+  // State from the renderer that is relevant to the overlay processor
+  // strategies.
+  struct CC_EXPORT RendererState {
+    RendererState();
+    ~RendererState();
+    float device_scale_factor;
+  };
   class CC_EXPORT Strategy {
    public:
     virtual ~Strategy() {}
@@ -24,7 +31,8 @@ class CC_EXPORT OverlayProcessor {
     // current set of render passes. Returns true if the strategy was successful
     // and adds any additional passes necessary to represent overlays to
     // |render_passes_in_draw_order|.
-    virtual bool Attempt(RenderPassList* render_passes_in_draw_order,
+    virtual bool Attempt(const RendererState& renderer_state,
+                         RenderPassList* render_passes_in_draw_order,
                          OverlayCandidateList* candidates) = 0;
   };
   typedef ScopedPtrVector<Strategy> StrategyList;
@@ -34,7 +42,8 @@ class CC_EXPORT OverlayProcessor {
   // Virtual to allow testing different strategies.
   virtual void Initialize();
 
-  void ProcessForOverlays(RenderPassList* render_passes_in_draw_order,
+  void ProcessForOverlays(const RendererState& renderer_state,
+                          RenderPassList* render_passes_in_draw_order,
                           OverlayCandidateList* candidate_list);
 
  protected: