media/gpu/chromeos: Change OOPVD to use STORAGE_DMABUFS

This lets us drop use of STORAGE_GPU_MEMORY_BUFFER VideoFrame. The
change is mostly semantics. GpuMemoryBuffer is being deprecated in
VideoFrame. ChromeOS out of process video decoding was the last major
user of the storage type, but it was only used to transport frames from
the video decoder utility process.

This removes DefaultFrameConverter in favor of a more explicit
converters: DmabufVideoFrameConverter and the test-only
GmbVideoFrameConverter. We can follow up with removing
GmbVideoFrameConverter in a later CL once a suitable replacement is
determined.

While this looks like it is removing some validations in
OOPVideoDecoder, those validations have been completely duplicated in
the VideoFrame mojo traits.

Bug: b:400455683
Change-Id: I90b7829522ff980ae23dab5a7b5dcb8dce4fe299
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6368475
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Nathan Hebert <nhebert@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1450241}