Update SkPicture cull rects with RTree information

src/core/SkBBoxHierarchy.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkBBoxHierarchy_DEFINED
 #define SkBBoxHierarchy_DEFINED
 
@@ skipping 16 matching lines @@
      */
     virtual void insert(const SkRect[], int N) = 0;
 
     /**
      * Populate results with the indices of bounding boxes interesecting that query.
      */
     virtual void search(const SkRect& query, SkTDArray<unsigned>* results) const = 0;
 
     virtual size_t bytesUsed() const = 0;
 
+    // Get the root bound.
+    virtual SkRect getRootBound() const = 0;
+
     SK_DECLARE_INST_COUNT(SkBBoxHierarchy)
 private:
     typedef SkRefCnt INHERITED;
 };
 
 #endif