share impl for setlength

Bug: skia:
Change-Id: I7d137547674d1352f38935504fd6f75cc7d7286f
Reviewed-on: https://skia-review.googlesource.com/128007
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed