Set willReadFragmentPosition on XP when doing a DstCopy.

src/gpu/GrPipeline.cpp

Index: src/gpu/GrPipeline.cpp
diff --git a/src/gpu/GrPipeline.cpp b/src/gpu/GrPipeline.cpp
index 906426caaaecc0699dd8d878ee2ccdfa9bdfd6dd..fc9f4eab12ecb1b4171bed990eca4f73841f0f10 100644
--- a/src/gpu/GrPipeline.cpp
+++ b/src/gpu/GrPipeline.cpp
@@ -112,13 +112,15 @@ void GrPipeline::adjustProgramFromOptimizations(const GrPipelineBuilder& pipelin
                                                 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) {