add a fast subset option and --dry-run

You can now pass files to rewrite, still defaulting
to all sources.  This speeds things up and is nice
for a Git or PRESUBMIT hook, added here too.

Passing --dry-run or -n will just check that the
files we would have written is the same, printing
the names of any mismatches and failing if any.

Cq-Include-Trybots: skia.primary:Housekeeper-PerCommit-CheckGeneratedFiles
Tricium: no
Change-Id: I94218f49071b8634841b04e4b536ad1ae5d9d5fd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/230143
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
2 files changed