Speed up InvalidationRegion

cc/base/invalidation_region.h

Index: cc/base/invalidation_region.h
diff --git a/cc/base/invalidation_region.h b/cc/base/invalidation_region.h
index 7aa4a8b2a3b7e7f53d4aee9a7f5c2c49ba0a9ef8..a9a0762bb445390482afea6a06037e257730c649 100644
--- a/cc/base/invalidation_region.h
+++ b/cc/base/invalidation_region.h
@@ -5,6 +5,8 @@
 #ifndef CC_BASE_INVALIDATION_REGION_H_
 #define CC_BASE_INVALIDATION_REGION_H_
 
+#include <vector>
+
 #include "cc/base/cc_export.h"
 #include "cc/base/region.h"
 #include "ui/gfx/geometry/rect.h"
@@ -22,12 +24,13 @@ class CC_EXPORT InvalidationRegion {
   void Swap(Region* region);
   void Clear();
   void Union(const gfx::Rect& rect);
-  bool IsEmpty() const { return region_.IsEmpty(); }
+  bool IsEmpty() const { return pending_rects_.empty() && region_.IsEmpty(); }
 
  private:
-  void SimplifyIfNeeded();
+  void FinalizePendingRects();
 
   Region region_;
+  std::vector<gfx::Rect> pending_rects_;
 };
 
 }  // namespace cc