impl SkSerial picture procs

The picture serialization code is a bit of a mess, with duplicated functions for streams and buffers.
Could not see how to fix that and land this at the same time, but I will try to circle back and
simplify if possible afterwards.

Bug: skia:
Change-Id: I9053fdc476c60f483df013d021e248258181c199
Reviewed-on: https://skia-review.googlesource.com/83943
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
9 files changed