commit to alpha bitmap procs

The alpha procs differ from the opaque ones only in a very isolated,
branch-predictable place.  If we need to make any of these care about
whether alphaScale == 256, we can probably just put a branch in there.

More refactoring to follow...

For now I've kept Clamp_S32_opaque_D32_nofilter_DX_shaderproc() around.

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I2739b6fc7d36c1adf6c702b271b20986f86e413f
Reviewed-on: https://skia-review.googlesource.com/c/171040
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Herb Derby <herb@google.com>
10 files changed