cc: Replace Region with SimpleEnclosedRegion for occlusion tracking

cc/base/region.h

Index: cc/base/region.h
diff --git a/cc/base/region.h b/cc/base/region.h
index 3ef32dbf3b32e1f871e9cd55fbddfb91d2575974..d78d4cb76ccb5fca6b9349287f35e3c431c839a9 100644
--- a/cc/base/region.h
+++ b/cc/base/region.h
@@ -7,7 +7,6 @@
 
 #include <string>
 
-#include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "cc/base/cc_export.h"
 #include "third_party/skia/include/core/SkRegion.h"
@@ -22,6 +21,7 @@ class TracedValue;
 }
 
 namespace cc {
+class SimpleEnclosedRegion;
 
 class CC_EXPORT Region {
  public:
@@ -47,6 +47,7 @@ class CC_EXPORT Region {
 
   void Subtract(const gfx::Rect& rect);
   void Subtract(const Region& region);
+  void Subtract(const SimpleEnclosedRegion& region);
   void Union(const gfx::Rect& rect);
   void Union(const Region& region);
   void Intersect(const gfx::Rect& rect);