hide virtual and rename to onMakeComposed

Bug: skia:
Change-Id: Ic18ee2af3273f81ebec9c9031162e808186c0acd
Reviewed-on: https://skia-review.googlesource.com/108300
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
15 files changed