move blend-row routines to SkBlitter_ARGB32.cpp

SkBlend::RowFactory is only ever used to pass these function
pointers from SkBlitMask_D32.cpp to SkBlitMask_ARGB32.cpp,
so let's eliminate the middleman.

Change-Id: If74af775bb3cdc3eec9dc4ebeb180ac42b184a54
Reviewed-on: https://skia-review.googlesource.com/c/170062
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
5 files changed