cc: Make occlusion a draw property.

cc/trees/occlusion.h

Index: cc/trees/occlusion.h
diff --git a/cc/trees/occlusion.h b/cc/trees/occlusion.h
index 56f9962df8b154493ea4fa192353cdf2bbc248e7..fec4915e2db3bccbaeb99b1124dacf52f9356919 100644
--- a/cc/trees/occlusion.h
+++ b/cc/trees/occlusion.h
@@ -5,6 +5,8 @@
 #ifndef CC_TREES_OCCLUSION_H_
 #define CC_TREES_OCCLUSION_H_
 
+#include <string>
+
 #include "base/basictypes.h"
 #include "cc/base/cc_export.h"
 #include "cc/base/simple_enclosed_region.h"
@@ -26,6 +28,9 @@ class CC_EXPORT Occlusion {
   bool IsOccluded(const gfx::Rect& content_rect) const;
   gfx::Rect GetUnoccludedContentRect(const gfx::Rect& content_rect) const;
 
+  bool IsEqual(const Occlusion& other) const;
+  std::string ToString() const;
+
  private:
   gfx::Rect GetUnoccludedRectInTargetSurface(
       const gfx::Rect& content_rect) const;