Add a new bench that tests a simple image filter DAG.

bench/ImageFilterDAGBench.cpp

Index: bench/ImageFilterDAGBench.cpp
diff --git a/bench/ImageFilterDAGBench.cpp b/bench/ImageFilterDAGBench.cpp
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index 0000000000000000000000000000000000000000..e6a3169507ea31b72951948983414bc523a98edb
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+++ b/bench/ImageFilterDAGBench.cpp
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+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkBenchmark.h"
+#include "SkBlurImageFilter.h"
+#include "SkMergeImageFilter.h"
+#include "SkCanvas.h"
+
+enum { kNumInputs = 5 };
+
+// Exercise a blur filter connected to 5 inputs of the same merge filter.
+// This bench shows an improvement in performance once cacheing of re-used
+// nodes is implemented, since the DAG is no longer flattened to a tree.
+
+class ImageFilterDAGBench : public SkBenchmark {
+public:
+    ImageFilterDAGBench() {
+    }
+
+protected:
+    virtual const char* onGetName() SK_OVERRIDE {
+        return "image_filter_dag";
+    }
+
+    virtual void onDraw(const int loops, SkCanvas* canvas) SK_OVERRIDE {
+        SkAutoTUnref<SkImageFilter> blur(SkBlurImageFilter::Create(20.0f, 20.0f));
+        SkImageFilter* inputs[kNumInputs];
+        for (int i = 0; i < kNumInputs; ++i) {
+            inputs[i] = blur.get();
+        }
+        SkAutoTUnref<SkImageFilter> merge(SkMergeImageFilter::Create(inputs, kNumInputs));
+        SkPaint paint;
+        paint.setImageFilter(merge);
+        SkRect rect = SkRect::Make(SkIRect::MakeWH(400, 400));
+        canvas->drawRect(rect, paint);
+    }
+
+private:
+    typedef SkBenchmark INHERITED;
+};
+
+DEF_BENCH(return new ImageFilterDAGBench;)