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 69e77cfc48348efe741b717ee11f31bd3b4eb1e5..7c9a130ec62f7049578ce317967194e879f97ca6 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -747,6 +747,9 @@ GrPorterDuffXPFactory::onCreateXferProcessor(const GrCaps& caps,
                                              const GrPipelineOptimizations& optimizations,
                                              bool hasMixedSamples,
                                              const DstTexture* dstTexture) const {
+    if (optimizations.fOverrides.fUsePLSDstRead) {

[bsalomon, 2016/01/04 15:33:47]

Maybe time to rename GrPipelineOptimizations... seems like this isn't an
optimization but rather a requirement for correct rendering.

+        return new ShaderPDXferProcessor(dstTexture, hasMixedSamples, fXfermode);
+    }
     BlendFormula blendFormula;
     if (optimizations.fCoveragePOI.isFourChannelOutput()) {
         if (SkXfermode::kSrcOver_Mode == fXfermode &&
@@ -806,6 +809,9 @@ void GrPorterDuffXPFactory::getInvariantBlendedColor(const GrProcOptInfo& colorP
 bool GrPorterDuffXPFactory::willReadDstColor(const GrCaps& caps,
                                              const GrPipelineOptimizations& optimizations,
                                              bool hasMixedSamples) const {
+    if (optimizations.fOverrides.fUsePLSDstRead) {
+        return true;
+    }
     if (caps.shaderCaps()->dualSourceBlendingSupport()) {
         return false;
     }
@@ -856,6 +862,9 @@ 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 &&