Optimize visualbench offscreen blits

tools/VisualBench/VisualSKPBench.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  *
  */
 
 #include "VisualSKPBench.h"
 
 #if SK_SUPPORT_GPU
 #include "GrContext.h"
 #endif
 
 VisualSKPBench::VisualSKPBench(const char* name, const SkPicture* pic)
     : fPic(SkRef(pic))
+    , fCullRect(fPic->cullRect().roundOut())
     , fName(name) {
     fUniqueName.printf("%s", name);
 }
 
 const char* VisualSKPBench::onGetName() {
     return fName.c_str();
 }
 
 const char* VisualSKPBench::onGetUniqueName() {
     return fUniqueName.c_str();
 }
 
 bool VisualSKPBench::isSuitableFor(Backend backend) {
     return backend != kNonRendering_Backend;
 }
 
+SkIPoint VisualSKPBench::onGetSize() {
+    return SkIPoint::Make(fCullRect.width(), fCullRect.height());
+}
+
 void VisualSKPBench::onDraw(int loops, SkCanvas* canvas) {
+    bool isOffset = SkToBool(fCullRect.left() | fCullRect.top());
+    if (isOffset) {
+        canvas->save();
+        canvas->translate(SkIntToScalar(-fCullRect.left()), SkIntToScalar(-fCullRect.top()));
+    }
+
     for (int i = 0; i < loops; i++) {
         canvas->drawPicture(fPic);
 #if SK_SUPPORT_GPU
         // Ensure the GrContext doesn't batch across draw loops.
         if (GrContext* context = canvas->getGrContext()) {
             context->flush();
         }
 #endif
     }
+
+    if (isOffset) {
+        canvas->restore();
+    }
 }