Image filters: force near-zero floating point parameters to zero.

src/effects/SkArithmeticMode.cpp

Index: src/effects/SkArithmeticMode.cpp
diff --git a/src/effects/SkArithmeticMode.cpp b/src/effects/SkArithmeticMode.cpp
index b8aa36853a52d33a2fe7718eb6eb39bfb637a98a..d51832eabcab5700628b00c4c2000348864879f0 100644
--- a/src/effects/SkArithmeticMode.cpp
+++ b/src/effects/SkArithmeticMode.cpp
@@ -21,10 +21,10 @@ class SkArithmeticMode_scalar : public SkXfermode {
 public:
     SkArithmeticMode_scalar(SkScalar k1, SkScalar k2, SkScalar k3, SkScalar k4,
                             bool enforcePMColor) {
-        fK[0] = k1;
-        fK[1] = k2;
-        fK[2] = k3;
-        fK[3] = k4;
+        fK[0] = SkScalarNormalize(k1);
+        fK[1] = SkScalarNormalize(k2);
+        fK[2] = SkScalarNormalize(k3);
+        fK[3] = SkScalarNormalize(k4);
         fEnforcePMColor = enforcePMColor;
     }