[skottie] Lazily-initialized default font manager

Only initialize a default font manager when needed.

Change-Id: I3473804d426f1f4981f3727d3539303fb670cdd1
Reviewed-on: https://skia-review.googlesource.com/150840
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
4 files changed