SkImage::onRefEncoded to return sk_sp.

This changes SkImage::onRefEncoded and downstack calls to return sk_sp.
All of the values returned are already sk_sp, so this just updates the
API. This change is currently behind the new flag
SK_IGNORE_SKIMAGE_ONREFENCODED_CHANGE so that Chromium can be updated.

Change-Id: Ic53a88ae23fa8b3b41b84c4abdc4b74e9879da38
Reviewed-on: https://skia-review.googlesource.com/128311
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
11 files changed