Fix stack buffer read overflow in GrConvolutionEffect::TestCreate.

src/gpu/effects/GrConvolutionEffect.cpp

Index: src/gpu/effects/GrConvolutionEffect.cpp
===================================================================
--- src/gpu/effects/GrConvolutionEffect.cpp	(revision 10813)
+++ src/gpu/effects/GrConvolutionEffect.cpp	(working copy)
@@ -227,8 +227,8 @@
                                       GrEffectUnitTest::kAlphaTextureIdx;
     Direction dir = random->nextBool() ? kX_Direction : kY_Direction;
     int radius = random->nextRangeU(1, kMaxKernelRadius);
-    float kernel[kMaxKernelRadius];
-    for (int i = 0; i < kMaxKernelRadius; ++i) {
+    float kernel[kMaxKernelWidth];
+    for (size_t i = 0; i < SK_ARRAY_COUNT(kernel); ++i) {
         kernel[i] = random->nextSScalar1();
     }
     float bounds[2];