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
new file mode 100644
index 0000000000000000000000000000000000000000..d693096998efdf3c078db78e8622fefff2f57e7b
--- /dev/null
+++ b/bench/ImageFilterDAGBench.cpp
@@ -0,0 +1,42 @@
+/*
+ * 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"
+
+#define NUM_COPIES 5

[Justin Novosad, 2014/04/10 15:51:28]

skia style: enum { kNumCopies = 5 };

[Stephen White, 2014/04/10 16:13:44]

Done.

+
+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[NUM_COPIES];
+        for (int i = 0; i < NUM_COPIES; ++i) {
+            inputs[i] = blur.get();

[Justin Novosad, 2014/04/10 15:51:28]

num copies is a misleading name.  You are not making a copy of blur. You are
just connecting it to multiple inputs.  num inputs?

[Stephen White, 2014/04/10 16:13:44]

Done.

+        }
+        SkAutoTUnref<SkImageFilter> merge(SkMergeImageFilter::Create(inputs, NUM_COPIES));
+        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;)