Refactor position computation to enable device space "nudge"

src/gpu/gl/builders/GrGLVertexShaderBuilder.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLVertexShader_DEFINED
 #define GrGLVertexShader_DEFINED
 
 #include "GrGLShaderBuilder.h"
 
 class GrGLVarying;
 
 class GrGLVertexBuilder : public GrGLShaderBuilder {
 public:
     GrGLVertexBuilder(GrGLProgramBuilder* program);
 
-    void transformToNormalizedDeviceSpace(const char* pos3);
+    void transformToNormalizedDeviceSpace(const GrShaderVar& posVar);
     void emitAttributes(const GrGeometryProcessor& gp);
 
     void addAttribute(const GrGeometryProcessor::Attribute* attr) {
         this->addAttribute(GrShaderVar(attr->fName,
                                        GrVertexAttribTypeToSLType(attr->fType),
                                        GrShaderVar::kAttribute_TypeModifier));
     }
 
 private:
     /*
@@ skipping 11 matching lines @@
     bool addAttribute(const GrShaderVar& var);
 
     const char* fRtAdjustName;
 
     friend class GrGLProgramBuilder;
 
     typedef GrGLShaderBuilder INHERITED;
 };
 
 #endif