The context used for Image creation was being used during orphaning. This
causes problems when the image is created with an external source or when
different contexts are used between creation and orphaning.

BUG=angleproject:3722

Change-Id: Iee4abd2116c3410efd8fb35722cc956cc6d8a3fa
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1709753Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>