ozone: Add overlay candidate implementation that queries support via IPC

Querying is done asynchronously, with a browser-side cache of responses.
GPU will try out the requested overlay configuration and report if it was
successful. Response delay is typically 1 frame but could be more in
rare situations. A maximum cache size is imposed so that a video that's being
moved/resized won't cause memory consumption to explode

TBR=danakj (trivial enum change)

Review URL: https://codereview.chromium.org/1157793004

Cr-Commit-Position: refs/heads/master@{#333073}

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