move SkMetaData into src

Bug: skia:
Change-Id: I3ef8c3ec0d6f33bd9a167b99313d6d313a748494
Reviewed-on: https://skia-review.googlesource.com/c/189284
Reviewed-by: Mike Reed <reed@google.com>
Auto-Submit: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
6 files changed