Add four_byte_interp benches.

bench/ColorPrivBench.cpp

+#include "SkBenchmark.h"
+#include "SkColorPriv.h"
+#include "SkRandom.h"
+#include "SkString.h"
+
+template <bool kFast, bool kScale>
+class FourByteInterpBench : public SkBenchmark {
+public:
+    FourByteInterpBench() {
+        fName.set("four_byte_interp");
+        fName.append(kFast ? "_fast" : "_slow");
+        fName.append(kScale ? "_255" : "_256");
+
+        // We'll exhaustively test all scales instead of using random numbers.
+        for (int i = 0; i <= 256; i++) {
+            fScales[i] = i;
+        }
+        if (kScale) fScales[256] = 255;  // We'll just do 255 twice if we're limited to [0,255].
+    }
+
+    virtual bool isSuitableFor(Backend backend) SK_OVERRIDE {
+        return backend == kNonRendering_Backend;
+    }
+
+    virtual const char* onGetName() SK_OVERRIDE { return fName.c_str(); }
+
+    virtual void onDraw(SkCanvas*) SK_OVERRIDE {
+        const SkPMColor src = 0xAB998877, dst = 0x66334455;
+        volatile SkPMColor junk = 0;
+        for (int i = 0; i < 10*this->getLoops(); ++i) {
+            for (size_t j = 0; j <= SK_ARRAY_COUNT(fScales); j++) {
+                const unsigned scale = fScales[j];
+                if (kFast && kScale) {
+                    junk ^= SkFastFourByteInterp(src, dst, scale);
+                } else if (kFast) {
+                    junk ^= SkFastFourByteInterp256(src, dst, scale);
+                } else if (kScale) {
+                    junk ^= SkFourByteInterp(src, dst, scale);
+                } else {
+                    junk ^= SkFourByteInterp256(src, dst, scale);
+                }
+            }
+        }
+    }
+
+private:
+    SkString fName;
+    unsigned fScales[257];  // We need space for [0, 256].
+};
+
+#define COMMA ,
+DEF_BENCH( return SkNEW(FourByteInterpBench<true COMMA true>); )
+DEF_BENCH( return SkNEW(FourByteInterpBench<true COMMA false>); )
+DEF_BENCH( return SkNEW(FourByteInterpBench<false COMMA true>); )
+DEF_BENCH( return SkNEW(FourByteInterpBench<false COMMA false>); )
+#undef COMMA