Add option to add precision to varyings in shader

src/gpu/gl/builders/GrGLFragmentShaderBuilder.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 GrGLFragmentShaderBuilder_DEFINED
 #define GrGLFragmentShaderBuilder_DEFINED
 #include "GrGLShaderBuilder.h"
@@ skipping 47 matching lines @@
     /** Returns a variable name that represents the position of the fragment in the FS. The position
         is in device space (e.g. 0,0 is the top left and pixel centers are at half-integers). */
     const char* fragmentPosition();
 
 private:
     /*
      * An internal call for GrGLFullProgramBuilder to use to add varyings to the vertex shader
      */
     void addVarying(GrSLType type,
                    const char* name,
-                   const char** fsInName);
+                   const char** fsInName,
+                   GrGLShaderVar::Precision fsPrecision = GrGLShaderVar::kDefault_Precision);
 
     /*
      * Private functions used by GrGLProgramBuilder for compilation
     */
     void bindProgramLocations(GrGLuint programId);
     bool compileAndAttachShaders(GrGLuint programId, SkTDArray<GrGLuint>* shaderIds) const;
     void emitCodeBeforeEffects();
     void emitCodeAfterEffects(const GrGLSLExpr4& inputColor, const GrGLSLExpr4& inputCoverage);
 
     /** Enables using the secondary color output and returns the name of the var in which it is
@@ skipping 30 matching lines @@
     bool fSetupFragPosition;
     bool fTopLeftFragPosRead;
 
     friend class GrGLProgramBuilder;
     friend class GrGLFullProgramBuilder;
 
     typedef GrGLShaderBuilder INHERITED;
 };
 
 #endif