add bench for gpu-image -> cpu-surface

bench/ImageBench.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 "Benchmark.h"
+#include "SkCanvas.h"
+#include "SkImage.h"
+#include "SkSurface.h"
+
+class GPU2RasterImageBench : public Benchmark {
+public:
+    GPU2RasterImageBench() {
+        fName.set("gpu2raster_image");
+    }
+
+    bool isSuitableFor(Backend backend) override {
+        return kGPU_Backend == backend;
+    }
+
+protected:
+    const char* onGetName() override {
+        return fName.c_str();
+    }
+
+    void onPerCanvasPreDraw(SkCanvas* canvas) override {
+        // create a gpu-backed Image
+        SkImageInfo info = SkImageInfo::MakeN32Premul(500, 500);
+        SkAutoTUnref<SkSurface> surface(canvas->newSurface(info));
+        canvas->drawColor(SK_ColorRED);
+        fGpuImage.reset(surface->newImageSnapshot());
+
+        // create a cpu-backed Surface
+        fRasterSurface.reset(SkSurface::NewRaster(info));
+    }
+
+    void onDraw(const int loops, SkCanvas*) override {
+        // Time drawing a gpu-image into a raster-surface
+        for (int i = 0; i < loops; i++) {
+            for (int inner = 0; inner < 10; ++inner) {
+                fRasterSurface->getCanvas()->drawImage(fGpuImage, 0, 0);
+            }
+        }
+    }
+
+private:
+    SkString                fName;
+    SkAutoTUnref<SkImage>   fGpuImage;
+    SkAutoTUnref<SkSurface> fRasterSurface;
+
+    typedef Benchmark INHERITED;
+};
+
+
+DEF_BENCH( return new GPU2RasterImageBench; )