[media] Use GpuVideoDecodeAcceleratorFactory in VDAVD.

This enables VdaVideoDecoder to construct VDAs for all platforms except Android.

Changes to enable VdaVideoDecoder on Mac are included; pass
--enable-features=MojoVideoDecoder to test.

Bug: 522298
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I99a37e43f7225bc11f134743b91c307f106cf7a3
Reviewed-on: https://chromium-review.googlesource.com/1011256
Commit-Queue: Dan Sanders <sandersd@chromium.org>
Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Frank Liberato <liberato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551451}
18 files changed