Change PromiseImage API to take GrContextThreadSafeProxy

This detaches PromiseImages from any specific context, just to
a certain family.

Next up is to remove the tileSpecificSKP code from the DDLTileHelper.

Currently we have this janky PromiseImageDummy GrImageContext that
we make for each promise image. It's not ideal but it'll tide us over.

Bug: skia:10286
Change-Id: I12ab0bb7df9360a08af594da80de9df14cc2a44f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/372516
Commit-Queue: Adlai Holler <adlai@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
13 files changed