added support for PLS path rendering

src/gpu/effects/GrCoverageSetOpXP.cpp

Index: src/gpu/effects/GrCoverageSetOpXP.cpp
diff --git a/src/gpu/effects/GrCoverageSetOpXP.cpp b/src/gpu/effects/GrCoverageSetOpXP.cpp
index 7761a6445ac14f91c2fda6984a387cc916ec2a27..abf4be0aa09de43d7879a9f4cc944fad475b954f 100644
--- a/src/gpu/effects/GrCoverageSetOpXP.cpp
+++ b/src/gpu/effects/GrCoverageSetOpXP.cpp
@@ -9,6 +9,7 @@
 #include "effects/GrCoverageSetOpXP.h"
 #include "GrCaps.h"
 #include "GrColor.h"
+#include "GrPipeline.h"
 #include "GrProcessor.h"
 #include "GrProcOptInfo.h"
 #include "glsl/GrGLSLBlend.h"
@@ -151,7 +152,6 @@ class ShaderCSOXferProcessor : public GrXferProcessor {
 public:
     ShaderCSOXferProcessor(const DstTexture* dstTexture,
                            bool hasMixedSamples,
-                           SkXfermode::Mode xfermode,
                            SkRegion::Op regionOp,
                            bool invertCoverage)
         : INHERITED(dstTexture, true, hasMixedSamples)
@@ -310,11 +310,17 @@ GrXPFactory* GrCoverageSetOpXPFactory::Create(SkRegion::Op regionOp, bool invert
     }
 }
 
+bool GrCoverageSetOpXPFactory::willReadDstColor(const GrCaps& caps,
+                                                const GrPipelineOptimizations& optimizations,
+                                                bool hasMixedSamples) const {
+    return optimizations.fOverrides.fUsePLSDstRead;
+}
+
 GrXferProcessor*
 GrCoverageSetOpXPFactory::onCreateXferProcessor(const GrCaps& caps,
                                                 const GrPipelineOptimizations& optimizations,
                                                 bool hasMixedSamples,
-                                                const DstTexture* dst) const {
+                                                const DstTexture* dst) const {    
     // We don't support inverting coverage with mixed samples. We don't expect to ever want this in
     // the future, however we could at some point make this work using an inverted coverage
     // modulation table. Note that an inverted table still won't work if there are coverage procs.
@@ -323,6 +329,9 @@ GrCoverageSetOpXPFactory::onCreateXferProcessor(const GrCaps& caps,
         return nullptr;
     }
 
+    if (optimizations.fOverrides.fUsePLSDstRead) {
+        return new ShaderCSOXferProcessor(dst, hasMixedSamples, fRegionOp, fInvertCoverage);
+    }
     return CoverageSetOpXP::Create(fRegionOp, fInvertCoverage);
 }