stop using SkScalarMul

BUG=skia:

Change-Id: Ie41d8665a1c62ba8eddc93d8cfefaf64ddc52ff8
Reviewed-on: https://skia-review.googlesource.com/8411
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Mike Reed <reed@google.com>
26 files changed