Optimize visualbench offscreen blits

tools/VisualBench/VisualBenchmarkStream.cpp

Index: tools/VisualBench/VisualBenchmarkStream.cpp
diff --git a/tools/VisualBench/VisualBenchmarkStream.cpp b/tools/VisualBench/VisualBenchmarkStream.cpp
index cfeff751967e52835b604c8655cb16047a0cd610..7f072e8ecbe0845f2d287f2342dfcf36a22b6701 100644
--- a/tools/VisualBench/VisualBenchmarkStream.cpp
+++ b/tools/VisualBench/VisualBenchmarkStream.cpp
@@ -39,9 +39,15 @@ class WarmupBench : public Benchmark {
 public:
     WarmupBench() {
         sk_tool_utils::make_big_path(fPath);
+        fPerlinRect = SkRect::MakeLTRB(0., 0., 400., 400.);
     }
 private:
     const char* onGetName() override { return "warmupbench"; }
+    SkIPoint onGetSize() override {
+        int w = SkScalarCeilToInt(SkTMax(fPath.getBounds().right(), fPerlinRect.right()));
+        int h = SkScalarCeilToInt(SkTMax(fPath.getBounds().bottom(), fPerlinRect.bottom()));
+        return SkIPoint::Make(w, h);
+    }
     void onDraw(int loops, SkCanvas* canvas) override {
         // We draw a big path to warm up the cpu, and then use perlin noise shader to warm up the
         // gpu
@@ -52,10 +58,9 @@ private:
         SkPaint perlinPaint;
         perlinPaint.setShader(SkPerlinNoiseShader::CreateTurbulence(0.1f, 0.1f, 1, 0,
                                                                     nullptr))->unref();
-        SkRect rect = SkRect::MakeLTRB(0., 0., 400., 400.);
         for (int i = 0; i < loops; i++) {
             canvas->drawPath(fPath, paint);
-            canvas->drawRect(rect, perlinPaint);
+            canvas->drawRect(fPerlinRect, perlinPaint);
 #if SK_SUPPORT_GPU
             // Ensure the GrContext doesn't batch across draw loops.
             if (GrContext* context = canvas->getGrContext()) {
@@ -65,6 +70,7 @@ private:
         }
     }
     SkPath fPath;
+    SkRect fPerlinRect;
 };
 
 VisualBenchmarkStream::VisualBenchmarkStream(const SkSurfaceProps& surfaceProps)