Add nanobench tests for BitmapRegionDecoder

bench/BitmapRegionDecoderBench.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef BitmapRegionDecoderBench_DEFINED
+#define BitmapRegionDecoderBench_DEFINED
+
+#include "Benchmark.h"
+#include "SkBitmapRegionDecoderInterface.h"
+#include "SkData.h"
+#include "SkImageInfo.h"
+#include "SkRefCnt.h"
+#include "SkString.h"
+
+/**
+ *  Time SkBitmapRegionDecoder.

[scroggo, 2015/09/18 15:07:23]

I think these comments could be improved. This one doesn't add much information.
The next paragraph says what this test doesn't do, and then the final paragraph
states what it does test.

I also think the comments should place more emphasis on the fact that this is to
compare scaling approaches.

[msarett, 2015/09/18 17:41:17]

You are right these comments are bad and actually misleading.  I do think this
matters as a subset test in addition to a scaling test.  Will fix.

+ *
+ *  The aim of this benchmark is not to duplicate the use cases that we test in the SubsetBenches.
+ *  Instead we assume that the SubsetBenches give us enough information to choose an appropriate
+ *  approach to subsetting.
+ *
+ *  This benchmark combines subsetting with scaling, allowing us to test the speed of several
+ *  different approaches to scaling while subsetting.
+ */
+class BitmapRegionDecoderBench : public Benchmark {

[scroggo, 2015/09/18 15:07:23]

If the primary goal here is to time approaches to scaling, maybe this should
have a name that better reflects that?

[msarett, 2015/09/18 17:41:17]

I'd prefer to stick with the name and improve the test.

+public:
+    // Calls encoded->ref()
+    BitmapRegionDecoderBench(const char* basename, SkData* encoded,
+            SkBitmapRegionDecoderInterface::Strategy strategy, SkColorType colorType,
+            uint32_t sampleSize, const SkIRect& subset);
+
+protected:
+    const char* onGetName() override;
+    bool isSuitableFor(Backend backend) override;
+    void onDraw(const int n, SkCanvas* canvas) override;
+    void onPreDraw() override;
+
+private:
+    SkString                                       fName;
+    SkAutoTDelete<SkBitmapRegionDecoderInterface>  fBRD;
+    SkAutoTUnref<SkData>                           fData;
+    const SkBitmapRegionDecoderInterface::Strategy fStrategy;
+    const SkColorType                              fColorType;
+    const uint32_t                                 fSampleSize;
+    const SkIRect                                  fSubset;
+    typedef Benchmark INHERITED;
+};
+#endif // BitmapRegionDecoderBench_DEFINED