Make all blending up to GrOptDrawState be handled by the xp/xp factory.

include/core/SkXfermode.h

Index: include/core/SkXfermode.h
diff --git a/include/core/SkXfermode.h b/include/core/SkXfermode.h
index 35e9837483ed098528beb89d64cc3fed2a3bbee1..05fd81152a72e1c6c2898991fd918641260c3566 100644
--- a/include/core/SkXfermode.h
+++ b/include/core/SkXfermode.h
@@ -217,10 +217,10 @@ public:
         or a fragment processor. This helper calls the asCoeff(), asXPFactory(),
         and asFragmentProcessor() virtuals. If the xfermode is NULL, it is treated as kSrcOver_Mode.
         It is legal to call this with all params NULL to simply test the return value.
-        fp, xpf, src, and dst must all be NULL or all non-NULL.
+        fp and xpf must both be NULL or all non-NULL.
      */
     static bool AsFragmentProcessorOrXPFactory(SkXfermode*, GrFragmentProcessor**,
-                                               GrXPFactory**, Coeff* src, Coeff* dst);
+                                               GrXPFactory**);
 
     SK_TO_STRING_PUREVIRT()
     SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()