Fix case where GrGLEffectMatrix gives back a dangling ptr for the coords var name.

src/effects/SkMatrixConvolutionImageFilter.cpp

Index: src/effects/SkMatrixConvolutionImageFilter.cpp
diff --git a/src/effects/SkMatrixConvolutionImageFilter.cpp b/src/effects/SkMatrixConvolutionImageFilter.cpp
index 37ca2fa141cae500dc19809c28ecd1e2dc6273ae..00bb6ec4bb474166f5ad7e62b69a72b83868e5ec 100644
--- a/src/effects/SkMatrixConvolutionImageFilter.cpp
+++ b/src/effects/SkMatrixConvolutionImageFilter.cpp
@@ -385,7 +385,7 @@ void GrGLMatrixConvolutionEffect::emitCode(GrGLShaderBuilder* builder,
                                            const char* outputColor,
                                            const char* inputColor,
                                            const TextureSamplerArray& samplers) {
-    const char* coords;
+    SkString coords;
     fEffectMatrix.emitCodeMakeFSCoords2D(builder, key, &coords);
     fImageIncrementUni = builder->addUniform(GrGLShaderBuilder::kFragment_ShaderType,
                                              kVec2f_GrSLType, "ImageIncrement");
@@ -407,7 +407,7 @@ void GrGLMatrixConvolutionEffect::emitCode(GrGLShaderBuilder* builder,
     int kHeight = fKernelSize.height();
 
     builder->fsCodeAppend("\t\tvec4 sum = vec4(0, 0, 0, 0);\n");
-    builder->fsCodeAppendf("\t\tvec2 coord = %s - %s * %s;\n", coords, target, imgInc);
+    builder->fsCodeAppendf("\t\tvec2 coord = %s - %s * %s;\n", coords.c_str(), target, imgInc);
     builder->fsCodeAppendf("\t\tfor (int y = 0; y < %d; y++) {\n", kHeight);
     builder->fsCodeAppendf("\t\t\tfor (int x = 0; x < %d; x++) {\n", kWidth);
     builder->fsCodeAppendf("\t\t\t\tfloat k = %s[y * %d + x];\n", kernel, kWidth);
@@ -426,7 +426,7 @@ void GrGLMatrixConvolutionEffect::emitCode(GrGLShaderBuilder* builder,
         builder->fsCodeAppendf("\t\t%s.rgb = clamp(%s.rgb, 0.0, %s.a);\n", outputColor, outputColor, outputColor);
     } else {
         builder->fsCodeAppend("\t\tvec4 c = ");
-        appendTextureLookup(builder, samplers[0], coords, fTileMode);
+        appendTextureLookup(builder, samplers[0], coords.c_str(), fTileMode);
         builder->fsCodeAppend(";\n");
         builder->fsCodeAppendf("\t\t%s.a = c.a;\n", outputColor);
         builder->fsCodeAppendf("\t\t%s.rgb = sum.rgb * %s + %s;\n", outputColor, gain, bias);