Remove the need for asCoeff in SkXfermode.

src/core/SkXfermode_proccoeff.h

 #ifndef SkXfermode_proccoeff_DEFINED
 #define SkXfermode_proccoeff_DEFINED
 
 #include "SkXfermode.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 
 struct ProcCoeff {
     SkXfermodeProc      fProc;
     SkXfermode::Coeff   fSC;
@@ skipping 14 matching lines @@
 
     virtual void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
                         const SkAlpha aa[]) const SK_OVERRIDE;
     virtual void xfer16(uint16_t dst[], const SkPMColor src[], int count,
                         const SkAlpha aa[]) const SK_OVERRIDE;
     virtual void xferA8(SkAlpha dst[], const SkPMColor src[], int count,
                         const SkAlpha aa[]) const SK_OVERRIDE;
 
     bool asMode(Mode* mode) const SK_OVERRIDE;
 
-    bool asCoeff(Coeff* sc, Coeff* dc) const SK_OVERRIDE;
+    bool supportsCoverageAsAlpha() const SK_OVERRIDE;
+
+    bool isOpaque(SkXfermode::SrcColorOpacity opacityType) const SK_OVERRIDE;
 
 #if SK_SUPPORT_GPU
     virtual bool asFragmentProcessor(GrFragmentProcessor**,
                                      GrTexture* background) const SK_OVERRIDE;
 
     virtual bool asXPFactory(GrXPFactory**) const SK_OVERRIDE;
 #endif
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkProcCoeffXfermode)
 
 protected:
     void flatten(SkWriteBuffer& buffer) const SK_OVERRIDE;
 
     Mode getMode() const { return fMode; }
 
     SkXfermodeProc getProc() const { return fProc; }
 
 private:
     SkXfermodeProc  fProc;
     Mode            fMode;
     Coeff           fSrcCoeff, fDstCoeff;
 
     friend class SkXfermode;
 
     typedef SkXfermode INHERITED;
 };
 
 #endif // #ifndef SkXfermode_proccoeff_DEFINED