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

src/effects/SkMorphologyImageFilter.cpp

Index: src/effects/SkMorphologyImageFilter.cpp
diff --git a/src/effects/SkMorphologyImageFilter.cpp b/src/effects/SkMorphologyImageFilter.cpp
index 33dd2e6ce8b21601d099ebd43c9cda4d69befbbf..6d15d4e2db80896772dc2e2346a218aac36b3540 100644
--- a/src/effects/SkMorphologyImageFilter.cpp
+++ b/src/effects/SkMorphologyImageFilter.cpp
@@ -324,7 +324,7 @@ void GrGLMorphologyEffect::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");
@@ -346,7 +346,7 @@ void GrGLMorphologyEffect::emitCode(GrGLShaderBuilder* builder,
     }
     const char* imgInc = builder->getUniformCStr(fImageIncrementUni);
 
-    builder->fsCodeAppendf("\t\tvec2 coord = %s - %d.0 * %s;\n", coords, fRadius, imgInc);
+    builder->fsCodeAppendf("\t\tvec2 coord = %s - %d.0 * %s;\n", coords.c_str(), fRadius, imgInc);
     builder->fsCodeAppendf("\t\tfor (int i = 0; i < %d; i++) {\n", this->width());
     builder->fsCodeAppendf("\t\t\t%s = %s(%s, ", outputColor, func, outputColor);
     builder->appendTextureLookup(GrGLShaderBuilder::kFragment_ShaderType, samplers[0], "coord");