Fix build

This fixes two issues with https://skia-review.googlesource.com/c/skia/+/91501:

1) The .fp files weren't updated to handle the move of proxyProvider to GrContextPriv
2) There were some missing guards for abandoned context's in the proxyprovider

Change-Id: I2a704ff2aec5f8f9a7ebaab9b8632abb5cf2e42c
Reviewed-on: https://skia-review.googlesource.com/92084
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
6 files changed