added support for PLS path rendering

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 c443e1e9925725e49cd6655191544d1cf92b75a3..cdd21627d4f9bda9a4f68c863273748f0e25eca3 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -739,6 +739,9 @@ GrPorterDuffXPFactory::onCreateXferProcessor(const GrCaps& caps,
                                              const GrPipelineOptimizations& optimizations,
                                              bool hasMixedSamples,
                                              const DstTexture* dstTexture) const {
+    if (optimizations.fOverrides.fUsePLSDstRead) {
+        return new ShaderPDXferProcessor(dstTexture, hasMixedSamples, fXfermode);
+    }
     BlendFormula blendFormula;
     if (optimizations.fCoveragePOI.isFourChannelOutput()) {
         if (SkXfermode::kSrcOver_Mode == fXfermode &&
@@ -798,6 +801,9 @@ void GrPorterDuffXPFactory::getInvariantBlendedColor(const GrProcOptInfo& colorP
 bool GrPorterDuffXPFactory::willReadDstColor(const GrCaps& caps,
                                              const GrPipelineOptimizations& optimizations,
                                              bool hasMixedSamples) const {
+    if (INHERITED::willReadDstColor(caps, optimizations, hasMixedSamples)) {
+        return true;
+    }
     if (caps.shaderCaps()->dualSourceBlendingSupport()) {
         return false;
     }
@@ -854,6 +860,9 @@ GrXferProcessor* GrPorterDuffXPFactory::CreateSrcOverXferProcessor(
         const GrPipelineOptimizations& optimizations,
         bool hasMixedSamples,
         const GrXferProcessor::DstTexture* dstTexture) {
+    if (optimizations.fOverrides.fUsePLSDstRead) {
+        return new ShaderPDXferProcessor(dstTexture, hasMixedSamples, SkXfermode::kSrcOver_Mode);
+    }
     if (!optimizations.fCoveragePOI.isFourChannelOutput() &&
         !(optimizations.fCoveragePOI.isSolidWhite() &&
           !hasMixedSamples &&