Use truncation, not rounding, when converting perlin noise seed (required by SVG spec).

src/effects/SkPerlinNoiseShader.cpp

Index: src/effects/SkPerlinNoiseShader.cpp
diff --git a/src/effects/SkPerlinNoiseShader.cpp b/src/effects/SkPerlinNoiseShader.cpp
index 5f858303c5772c9d8096cd32d1132260682faed6..77ce9cb3482346a5ebc719afdad8954146ccbfc1 100644
--- a/src/effects/SkPerlinNoiseShader.cpp
+++ b/src/effects/SkPerlinNoiseShader.cpp
@@ -124,8 +124,9 @@ public:
     {
         static const SkScalar gInvBlockSizef = SkScalarInvert(SkIntToScalar(kBlockSize));
 
+        // According to the SVG spec, we must truncate (not round) the seed value.
+        fSeed = SkScalarTruncToInt(seed);
         // The seed value clamp to the range [1, kRandMaximum - 1].
-        fSeed = SkScalarRoundToInt(seed);
         if (fSeed <= 0) {
             fSeed = -(fSeed % (kRandMaximum - 1)) + 1;
         }