Fix bug in reads fragment position on gpu.

src/gpu/GrPipeline.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrPipeline.h"
 
 #include "GrCaps.h"
@@ skipping 175 matching lines @@
                                                 const GrProcOptInfo& colorPOI,
                                                 const GrProcOptInfo& coveragePOI,
                                                 int* firstColorProcessorIdx,
                                                 int* firstCoverageProcessorIdx) {
     fReadsFragPosition = fXferProcessor->willReadFragmentPosition();
 
     if ((flags & GrXferProcessor::kIgnoreColor_OptFlag) ||
         (flags & GrXferProcessor::kOverrideColor_OptFlag)) {
         *firstColorProcessorIdx = pipelineBuilder.numColorFragmentProcessors();
     } else {
-        if (coveragePOI.readsFragPosition()) {
+        if (colorPOI.readsFragPosition()) {
             fReadsFragPosition = true;
         }
     }
 
     if (flags & GrXferProcessor::kIgnoreCoverage_OptFlag) {
         *firstCoverageProcessorIdx = pipelineBuilder.numCoverageFragmentProcessors();
     } else {
         if (coveragePOI.readsFragPosition()) {
             fReadsFragPosition = true;
         }
@@ skipping 21 matching lines @@
     }
 
     for (int i = 0; i < a.numFragmentProcessors(); i++) {
         if (!a.getFragmentProcessor(i).isEqual(b.getFragmentProcessor(i), ignoreCoordTransforms)) {
             return false;
         }
     }
     return true;
 }