Migrate scenic_gpu_*.mojom to new Mojo types

* There are some other changes to the code logic, derived from the
usage of PendingRemote in function arguments instead of InterfacePtr.
* Shorthands provided by the new Mojo types allowed to simplify some
* Moved initialization of affected members to their declarations,
where possible, to comply with coding guidelines.

Bug: 955171
Change-Id: Iebdc315dfcfebc671e0c91c9cf4f9fdd9fdf7b24
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1847309
Reviewed-by: Mario Sanchez Prada <mario@igalia.com>
Reviewed-by: Michael Spang <spang@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Oksana Zhuravlova <oksamyt@chromium.org>
Commit-Queue: Jacobo Aragunde Pérez <jaragunde@igalia.com>
Cr-Commit-Position: refs/heads/master@{#710313}
6 files changed