Add interface to SkXfermode to return a GrEffect and blend coeffs.

src/core/SkXfermode.cpp

Index: src/core/SkXfermode.cpp
===================================================================
--- src/core/SkXfermode.cpp	(revision 8410)
+++ src/core/SkXfermode.cpp	(working copy)
@@ -680,6 +680,22 @@
     return false;
 }
 
+bool SkXfermode::asNewEffect(GrContext*, GrEffectRef**, Coeff*, Coeff*) const {
+    return false;
+}
+
+bool SkXfermode::AsNewEffect(SkXfermode* xfermode,
+                             GrContext* context,
+                             GrEffectRef** effect,
+                             Coeff* src,
+                             Coeff* dst) {
+    if (NULL == xfermode) {

[robertphillips, 2013/03/27 18:12:09]

do we need to set 'effect' to be NULL as part of the contract?

[bsalomon, 2013/03/27 18:39:42]

Yes, will add that.

+        return ModeAsCoeff(kSrcOver_Mode, src, dst);
+    } else {
+        return xfermode->asNewEffect(context, effect, src, dst);
+    }
+}
+
 SkPMColor SkXfermode::xferColor(SkPMColor src, SkPMColor dst) const{
     // no-op. subclasses should override this
     return dst;
@@ -958,6 +974,10 @@
         return true;
     }
 
+    virtual bool asNewEffect(GrContext*, GrEffectRef**, Coeff* src, Coeff* dst) const SK_OVERRIDE {
+        return this->asCoeff(src, dst);
+    }
+
     SK_DEVELOPER_TO_STRING()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkProcCoeffXfermode)