Optimize visualbench offscreen blits

tools/VisualBench/VisualSKPBench.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  */
 
 #ifndef VisualSKPBench_DEFINED
 #define VisualSKPBench_DEFINED
 
 #include "Benchmark.h"
 #include "SkCanvas.h"
 #include "SkPicture.h"
 
 /**
  * Runs an SkPicture as a benchmark by repeatedly drawing it
  */
 class VisualSKPBench : public Benchmark {
 public:
     VisualSKPBench(const char* name, const SkPicture*);
 
 protected:
     const char* onGetName() override;
     const char* onGetUniqueName() override;
     bool isSuitableFor(Backend backend) override;
+    SkIPoint onGetSize() override;
     void onDraw(int loops, SkCanvas* canvas) override;
 
 private:
     SkAutoTUnref<const SkPicture> fPic;
+    SkIRect fCullRect;
     SkString fName;
     SkString fUniqueName;
 
     typedef Benchmark INHERITED;
 };
 
 #endif