media/gpu: Support keyframeless VP9 resolution changes for testing

VP9 verification sets "frm_resize" and "sub8x8_sf" [1] change
resolutions mid-stream without Key-frames. This is an arcane
feature and rare in the wild, where the rule is to have keyframes
to signal new resolutions.

ToT VP9Decoder considers any resolution changes a kConfigChange,
which causes the client to drop reference frames and reallocate
surfaces and context(s). But VA-API VideoDecoders on Intel and
AMD do support reusing the current context and surfaces for
smaller resolutions; https://crrev.com/c/4032552 did just that,
hence verifying the test vectors, but breaking DRM overlays ([2]),
so it was reverted.

In the large scheme of things, though, we'd rather reallocate the
context and surfaces when the resolution decreases (to have a
smaller mem footprint, not to mention to keep DRM overlays working),
rather than reusing things just to satisfy a theoretical concern.

So after a few tries at fixing this in code ([3,4] - ugly stuff),
I decided to give up and take up the suggestion in [5] to make
this a test only feature. With that, this CL adds a test flag and
sets it from v_d_a_tests code.

[1] https://www.webmproject.org/vp9/levels/#test-descriptions
[2] I dug into this for a while and I believe this was due to
VAAPI reusing |coded_size| and reducing the visible area while
the DRM API really needed both to be accurate. Maybe I'll dig
some more and try to find a repro case to file a bug.
Also note that FFmpeg+VA_API does support this non-reallocation
mode but would have the same DRM overlays issue if it was to
support them.
[3] https://crrev.com/c/4409593
[4] https://crrev.com/c/4437095
[5] https://crrev.com/c/4409593/2/media/gpu/vaapi/vaapi_video_decoder.cc#1145

Bug: b:207057398

Change-Id: Idb920f9e8e12704148cacc68befd5c5fb480e0ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4444189
Commit-Queue: Miguel Casas-Sanchez <mcasas@chromium.org>
Reviewed-by: Andres Calderon Jaramillo <andrescj@chromium.org>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1135030}

• media/gpu/chromeos/video_decoder_pipeline.cc[diff]
• media/gpu/chromeos/video_decoder_pipeline.h[diff]
• media/gpu/test/video_decode_accelerator_tests.cc[diff]
• media/gpu/test/video_player/decoder_wrapper.cc[diff]
• media/gpu/test/video_player/decoder_wrapper.h[diff]
• media/gpu/vaapi/vaapi_video_decoder.cc[diff]
• media/gpu/vaapi/vaapi_video_decoder.h[diff]
• media/gpu/vp9_decoder.cc[diff]
• media/gpu/vp9_decoder.h[diff]