Implement Porter Duff XP with a blend table

include/gpu/GrColor.h

Index: include/gpu/GrColor.h
diff --git a/include/gpu/GrColor.h b/include/gpu/GrColor.h
index 43bfd8dc11e0aa104d83c4c998efc4e50909f202..05d14455a9c0fdda9998545a7cce6304146c59b9 100644
--- a/include/gpu/GrColor.h
+++ b/include/gpu/GrColor.h
@@ -142,6 +142,8 @@ enum GrColorComponentFlags {
     kB_GrColorComponentFlag = 1 << (GrColor_SHIFT_B / 8),
     kA_GrColorComponentFlag = 1 << (GrColor_SHIFT_A / 8),
 
+    kNone_GrColorComponentFlags = 0,
+
     kRGB_GrColorComponentFlags = (kR_GrColorComponentFlag | kG_GrColorComponentFlag |
                                   kB_GrColorComponentFlag),
 
@@ -149,6 +151,8 @@ enum GrColorComponentFlags {
                                    kB_GrColorComponentFlag | kA_GrColorComponentFlag)
 };
 
+GR_MAKE_BITFIELD_OPS(GrColorComponentFlags)
+
 static inline char GrColorComponentFlagToChar(GrColorComponentFlags component) {
     SkASSERT(SkIsPow2(component));
     switch (component) {