cc: Make occlusion a draw property.

cc/trees/occlusion.cc

Index: cc/trees/occlusion.cc
diff --git a/cc/trees/occlusion.cc b/cc/trees/occlusion.cc
index 14168f9699f11eddaab5c9af683fbcddccea81b9..6a7149627473f8e376d9fe8d45d64c15475136c9 100644
--- a/cc/trees/occlusion.cc
+++ b/cc/trees/occlusion.cc
@@ -85,4 +85,16 @@ gfx::Rect Occlusion::GetUnoccludedRectInTargetSurface(
   return unoccluded_rect_in_target_surface;
 }
 
+bool Occlusion::IsEqual(const Occlusion& other) const {
+  return draw_transform_ == other.draw_transform_ &&
+         occlusion_from_inside_target_ == other.occlusion_from_inside_target_ &&
+         occlusion_from_outside_target_ == other.occlusion_from_outside_target_;
+}
+
+std::string Occlusion::ToString() const {
+  return draw_transform_.ToString() + "outside(" +
+         occlusion_from_outside_target_.ToString() + ") inside(" +
+         occlusion_from_inside_target_.ToString() + ")";
+}
+
 }  // namespace cc