Use noperspective interpolation for 2D draws

src/gpu/glsl/GrGLSLShaderBuilder.h

Index: src/gpu/glsl/GrGLSLShaderBuilder.h
diff --git a/src/gpu/glsl/GrGLSLShaderBuilder.h b/src/gpu/glsl/GrGLSLShaderBuilder.h
index 16a07563060c58b087826b89220eed5f3c939557..fa1b8e6c2f4f2ad7d5585a838fb815e15e9b6759 100644
--- a/src/gpu/glsl/GrGLSLShaderBuilder.h
+++ b/src/gpu/glsl/GrGLSLShaderBuilder.h
@@ -122,6 +122,19 @@ protected:
     typedef GrTAllocator<GrGLSLShaderVar> VarArray;
     void appendDecls(const VarArray& vars, SkString* out) const;
 
+    /**
+     * Features that should only be enabled internally by the builders.
+     */
+    enum GLSLPrivateFeature {
+        kFragCoordConventions_GLSLPrivateFeature,
+        kBlendEquationAdvanced_GLSLPrivateFeature,
+        kBlendFuncExtended_GLSLPrivateFeature,
+        kExternalTexture_GLSLPrivateFeature,
+        kFramebufferFetch_GLSLPrivateFeature,
+        kNoPerspectiveInterpolation_GLSLPrivateFeature,
+        kLastGLSLPrivateFeature = kNoPerspectiveInterpolation_GLSLPrivateFeature
+    };
+
     /*
      * A general function which enables an extension in a shader if the feature bit is not present
      */
@@ -193,6 +206,7 @@ protected:
 
     friend class GrGLSLProgramBuilder;
     friend class GrGLProgramBuilder;
+    friend class GrGLSLVaryingHandler; // to access noperspective interpolation feature.
     friend class GrGLPathProgramBuilder; // to access fInputs.
     friend class GrVkProgramBuilder;
 };