Make GrGLShaderBuilder check whether GrEffect advertised that it would require the dst color or frag

src/gpu/GrAAHairLinePathRenderer.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrAAHairLinePathRenderer.h"
 
@@ skipping 648 matching lines @@
 
         virtual void setData(const GrGLUniformManager&, const GrDrawEffect&) SK_OVERRIDE {}
 
     private:
         typedef GrGLEffect INHERITED;
     };
 
 private:
     HairLineEdgeEffect() {
         this->addVertexAttrib(kVec4f_GrSLType);
+        this->setWillReadFragmentPosition();
     }
 
     virtual bool onIsEqual(const GrEffect& other) const SK_OVERRIDE {
         return true;
     }
 
     GR_DECLARE_EFFECT_TEST;
 
     typedef GrEffect INHERITED;
 };
@@ skipping 159 matching lines @@
                             4 * lineCnt + kVertsPerQuad*quads, // startV
                             0,                                 // startI
                             kVertsPerQuad*n,                   // vCount
                             kIdxsPerQuad*n);                   // iCount
         quads += n;
     }
     target->resetIndexSource();
 
     return true;
 }