Some backends may change state while initializing resources.  Make sure
that all resources are initialized before synchronizing the backend
state for the given operation.

BUG=angleproject:2107

Change-Id: Ie75ac3eee986e41dfe3dd11a94a706e19df7497e
Reviewed-on: https://chromium-review.googlesource.com/678481
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>