Set willReadFragmentPosition on XP when doing a DstCopy.

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 "GrBatch.h"
@@ skipping 94 matching lines @@
     fInitBT.fCanTweakAlphaForCoverage =
         SkToBool(optFlags & GrXferProcessor::kCanTweakAlphaForCoverage_OptFlag);
 }
 
 void GrPipeline::adjustProgramFromOptimizations(const GrPipelineBuilder& pipelineBuilder,
                                                 GrXferProcessor::OptFlags flags,
                                                 const GrProcOptInfo& colorPOI,
                                                 const GrProcOptInfo& coveragePOI,
                                                 int* firstColorStageIdx,
                                                 int* firstCoverageStageIdx) {
-    fReadsFragPosition = false;
+    fReadsFragPosition = fXferProcessor->willReadFragmentPosition();
 
     if ((flags & GrXferProcessor::kIgnoreColor_OptFlag) ||
         (flags & GrXferProcessor::kOverrideColor_OptFlag)) {
         *firstColorStageIdx = pipelineBuilder.numColorFragmentStages();
     } else {
-        fReadsFragPosition = colorPOI.readsFragPosition();
+        if (coveragePOI.readsFragPosition()) {
+            fReadsFragPosition = true;
+        }
     }
 
     if (flags & GrXferProcessor::kIgnoreCoverage_OptFlag) {
         *firstCoverageStageIdx = pipelineBuilder.numCoverageFragmentStages();
     } else {
         if (coveragePOI.readsFragPosition()) {
             fReadsFragPosition = true;
         }
     }
 }
@@ skipping 19 matching lines @@
     SkASSERT(this->numFragmentStages() == that.numFragmentStages());
     for (int i = 0; i < this->numFragmentStages(); i++) {
 
         if (this->getFragmentStage(i) != that.getFragmentStage(i)) {
             return false;
         }
     }
     return true;
 }