Implement Porter Duff XP with a blend table

src/gpu/GrCaps.cpp

Index: src/gpu/GrCaps.cpp
diff --git a/src/gpu/GrCaps.cpp b/src/gpu/GrCaps.cpp
index 625bd90e8f5adc45b88c0d59cad0d3d1648f1c09..f078fad9fb1851867612d858e5623fa964b8554c 100644
--- a/src/gpu/GrCaps.cpp
+++ b/src/gpu/GrCaps.cpp
@@ -73,8 +73,8 @@ SkString GrShaderCaps::dump() const {
     return r;
 }
 
-void GrShaderCaps::applyOptionsOverrides(const GrContextOptions&) {
-    // Currently no overrides apply to shader caps.
+void GrShaderCaps::applyOptionsOverrides(const GrContextOptions& options) {
+    fDualSourceBlendingSupport = fDualSourceBlendingSupport && !options.fSuppressDualSourceBlending;
 }
 
 ///////////////////////////////////////////////////////////////////////////////