Implement support for mixed sampled render targets

src/gpu/effects/GrPorterDuffXferProcessor.cpp

Index: src/gpu/effects/GrPorterDuffXferProcessor.cpp
diff --git a/src/gpu/effects/GrPorterDuffXferProcessor.cpp b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
index 2735ac3c22eceefc9049a382c4c751a746a1d23b..7531f2e16e5b5255779ae2ba1a2958bebc6694b7 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -402,7 +402,8 @@ PorterDuffXferProcessor::internalGetOptimizations(const GrProcOptInfo& colorPOI,
     // has to read at all. If not, we'll disable blending.
     if (!hasCoverage) {
         if (dstCoeffIsZero) {
-            if (kOne_GrBlendCoeff == fSrcBlend) {
+            if (kOne_GrBlendCoeff == fSrcBlend &&
+                !colorPOI.hasMixedSamplesModulation()) {
                 // if there is no coverage and coeffs are (1,0) then we
                 // won't need to read the dst at all, it gets replaced by src
                 fDstBlend = kZero_GrBlendCoeff;