This maintains some forward declarations so all >400 uses don't need to be
updated at the same time.

This patch changes all forward declarations and code that depends on them.

BUG=763556
TBR=stevenjb@chromium.org (chromeos/network)

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: Icabd948fe9e0881fdb60db38b31a9d0763867bc4
Reviewed-on: https://chromium-review.googlesource.com/657249


Reviewed-by: Brett Wilson <brettw@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501092}