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

src/effects/SkArithmeticMode.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkArithmeticMode.h"
 #include "SkColorPriv.h"
 #include "SkFlattenableBuffers.h"
@@ skipping 333 matching lines @@
 void GrGLArithmeticEffect::emitCode(GrGLShaderBuilder* builder,
                                     const GrDrawEffect& drawEffect,
                                     EffectKey key,
                                     const char* outputColor,
                                     const char* inputColor,
                                     const TextureSamplerArray& samplers) {
 
     GrTexture* backgroundTex = drawEffect.castEffect<GrArithmeticEffect>().backgroundTexture();
     const char* dstColor;
     if (backgroundTex) {
-        const char* bgCoords;
+        SkString bgCoords;
         GrSLType bgCoordsType = fBackgroundEffectMatrix.emitCode(builder, key, &bgCoords, NULL, "BG");
         builder->fsCodeAppend("\t\tvec4 bgColor = ");
         builder->appendTextureLookup(GrGLShaderBuilder::kFragment_ShaderType,
                                      samplers[0],
-                                     bgCoords,
+                                     bgCoords.c_str(),
                                      bgCoordsType);
         builder->fsCodeAppendf(";\n");
         dstColor = "bgColor";
     } else {
         dstColor = builder->dstColor();
     }
 
     SkASSERT(NULL != dstColor);
     fKUni = builder->addUniform(GrGLShaderBuilder::kFragment_ShaderType,
                                 kVec4f_GrSLType, "k");
@@ skipping 76 matching lines @@
                                              background);
     }
     return true;
 }
 
 #endif
 
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkArithmeticMode)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkArithmeticMode_scalar)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END