rename some flattenable routines

Initialize felt a little too nebulous, and I think
the verb for "define registrar entry" is "register".

Change-Id: I52f2eb5df5acd46a8b38bb9ea9bb07f4ac8f3789
Reviewed-on: https://skia-review.googlesource.com/c/163990
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
45 files changed