Add SkRasterPipeline blitter.

src/core/SkXfermode.cpp

Index: src/core/SkXfermode.cpp
diff --git a/src/core/SkXfermode.cpp b/src/core/SkXfermode.cpp
index e91f53a6cc5a101ed1c022621dfb60699e810595..924656869973b1157cd2337ad66b96002023aa38 100644
--- a/src/core/SkXfermode.cpp
+++ b/src/core/SkXfermode.cpp
@@ -1420,6 +1420,14 @@ bool SkXfermode::IsOpaque(const SkXfermode* xfer, SrcColorOpacity opacityType) {
     return xfer->isOpaque(opacityType);
 }
 
+bool SkXfermode::appendStages(SkRasterPipeline* pipeline) const {
+    return this->onAppendStages(pipeline);
+}
+
+bool SkXfermode::onAppendStages(SkRasterPipeline*) const {
+    return false;
+}
+
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkXfermode)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkProcCoeffXfermode)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END