Reland "Add SharedImage identifying bit to gpu::Mailbox"

This is a reland of e4f5071361d8ccc668599d9a47afa8c4b0c7faeb

There was a conflict between this CL and the one which landed at the
same time:
https://chromium-review.googlesource.com/c/chromium/src/+/1415306

Re-landing this first.

Original change's description:
> Add SharedImage identifying bit to gpu::Mailbox
>
> As we transition to SharedImage, certain places in code need to know
> whether a mailbox they receive should be used with the SharedImage
> system or legacy mailbox system.
>
> This CL adds a flag to Mailbox to identify SharedImage usage, and
> converts existing clients to check this flag.
>
> Bug: 922834
> Change-Id: I20900e302e2620d216377edc5d6f0017270c23d6
> Reviewed-on: https://chromium-review.googlesource.com/c/1416836
> Commit-Queue: Eric Karl <ericrk@chromium.org>
> Reviewed-by: Antoine Labour <piman@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#624883}

Bug: 922834
Change-Id: Iaf0aaddfbf8d69eebe9d9c325826dc5c1879cb9c
Reviewed-on: https://chromium-review.googlesource.com/c/1430992
Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Eric Karl <ericrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625302}
16 files changed