cut out the rest of blend modes in flutter

SkXfermode_opts.h is moot when SK_FORCE_RASTER_PIPELINE_BLITTER is
defined.  There are a couple other blitters and routines and things
that are also just there for 565/8888 performance, so I think we
can just turn on SK_FORCE_RASTER_PIPELINE_BLITTER and start guarding
the rest of them similarly.

Looks like maybe cuts another 13K?

Change-Id: Ib3894b07da649a93e93b6a4cb7686772a57b6def
Reviewed-on: https://skia-review.googlesource.com/c/164181
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/gn/flutter_defines.gni b/gn/flutter_defines.gni
index d7ef0e3..adce3e5 100644
--- a/gn/flutter_defines.gni
+++ b/gn/flutter_defines.gni
@@ -14,4 +14,5 @@
   # Fast low-precision software rendering isn't a priority for Flutter.
   "SK_DISABLE_LEGACY_SHADERCONTEXT",
   "SK_DISABLE_LOWP_RASTER_PIPELINE",
+  "SK_FORCE_RASTER_PIPELINE_BLITTER",
 ]
diff --git a/src/opts/SkXfermode_opts.h b/src/opts/SkXfermode_opts.h
index a8b0268..5c35991 100644
--- a/src/opts/SkXfermode_opts.h
+++ b/src/opts/SkXfermode_opts.h
@@ -13,6 +13,14 @@
 #include "SkNx.h"
 #include "SkXfermodePriv.h"
 
+#ifdef SK_FORCE_RASTER_PIPELINE_BLITTER
+
+namespace SK_OPTS_NS {
+    /*not static*/ inline SkXfermode* create_xfermode(SkBlendMode) { return nullptr; }
+}
+
+#else
+
 namespace {
 
 // Most xfermodes can be done most efficiently 4 pixels at a time in 8 or 16-bit fixed point.
@@ -125,4 +133,6 @@
 
 } // namespace SK_OPTS_NS
 
+#endif // #ifdef SK_FORCE_RASTER_PIPELINE_BLITTER
+
 #endif//Sk4pxXfermode_DEFINED