Fixing some warnings on Linux

src/gpu/gl/GrGLShaderBuilder.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gl/GrGLShaderBuilder.h"
 #include "gl/GrGLProgram.h"
 #include "gl/GrGLUniformHandle.h"
@@ skipping 84 matching lines @@
     , fUniformManager(uniformManager)
     , fCurrentStageIdx(kNonStageIdx)
     , fSetupFragPosition(false)
     , fRTHeightUniform(GrGLUniformManager::kInvalidUniformHandle) {
 
     fPositionVar = &fVSAttrs.push_back();
     fPositionVar->set(kVec2f_GrSLType, GrGLShaderVar::kAttribute_TypeModifier, "aPosition");
 }
 
 void GrGLShaderBuilder::codeAppendf(ShaderType type, const char format[], va_list args) {
-    SkString* string;
+    SkString* string = NULL;
     switch (type) {
         case kVertex_ShaderType:
             string = &fVSCode;
             break;
         case kGeometry_ShaderType:
             string = &fGSCode;
             break;
         case kFragment_ShaderType:
             string = &fFSCode;
             break;
         default:
             GrCrash("Invalid shader type");
     }
     string->appendf(format, args);
 }
 
 void GrGLShaderBuilder::codeAppend(ShaderType type, const char* str) {
-    SkString* string;
+    SkString* string = NULL;
     switch (type) {
         case kVertex_ShaderType:
             string = &fVSCode;
             break;
         case kGeometry_ShaderType:
             string = &fGSCode;
             break;
         case kFragment_ShaderType:
             string = &fFSCode;
             break;
@@ skipping 367 matching lines @@
                        key,
                        vsInCoord,
                        fsOutColor,
                        fsInColor,
                        textureSamplers);
     this->fVSCode.appendf("\t}\n");
     this->fFSCode.appendf("\t}\n");
 
     return glEffect;
 }