Implement Porter Duff XP with a blend table

include/gpu/GrContextOptions.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrContextOptions_DEFINED
 #define GrContextOptions_DEFINED
 
 #include "SkTypes.h"
 
 struct GrContextOptions {
     GrContextOptions()
         : fDrawPathToCompressedTexture(false)
         , fSuppressPrints(false)
-        , fMaxTextureSizeOverride(SK_MaxS32) {}
+        , fMaxTextureSizeOverride(SK_MaxS32)
+        , fSuppressDualSourceBlending(false) {}
 
     // EXPERIMENTAL
     // May be removed in the future, or may become standard depending
     // on the outcomes of a variety of internal tests.
     bool fDrawPathToCompressedTexture;
 
     // Suppress prints for the GrContext.
     bool fSuppressPrints;
 
     /** Overrides: These options override feature detection using backend API queries. These
         overrides can only reduce the feature set or limits, never increase them beyond the
         detected values. */
 
-    int fMaxTextureSizeOverride;
+    int  fMaxTextureSizeOverride;
+    bool fSuppressDualSourceBlending;
 };
 
 #endif