GitLab

This adds *SharedMemoryRegion create methods that parallel those in
base::. These use mojo::SharedMemoryBuffer::Create, which will use a
broker if appropriate to create shared memory in unprivileged processes.

Also update comments to clarify migration.

Bug: 872778
Change-Id: Ia32da8181fd37d88a49a26e3e7e158612147646b
Reviewed-on: https://chromium-review.googlesource.com/1169602Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585068}