Cherry pick PR #9309: android: Optimize av1 codec initialization

[cobalt-github-releaser-bot]

Refer to the original PR: #9309

Introduce a feature flag to enable optimized AV1 codec initialization.
When enabled, detect if the device supports AV1 only up to 8K30.
If so, defer codec initialization until the video's actual frame rate
is known.

Bug: 486980027

[cobalt-github-releaser-bot]

Caution

There were merge conflicts while cherry picking! Check out cherry-pick-main-9309 and fix the conflicts before proceeding. Check the log at https://github.com/youtube/cobalt/actions/runs/24421533252 for details.

[github-actions]

🤖 Gemini Suggested Commit Message

---

android: Optimize AV1 codec initialization

Introduce a feature flag, kEnableAv1StartupOptimization, to defer AV1
codec initialization until the video's actual frame rate is known.
This optimization is enabled if the device supports AV1 only up to 8K30.
Deferring initialization prevents accidental 8K60 usage and exceeding
system resource limits on devices with limited AV1 8K capabilities.

Additionally, clear the media capabilities cache when the display or
audio output device changes to ensure accurate capability detection.

Bug: 486980027

---

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[gemini-code-assist]

Code Review

This pull request introduces an optimization for AV1 playback on Android devices that support 8K at 30fps but not 60fps. It adds a mechanism in MediaCapabilitiesCache to detect this cap and updates MediaCodecVideoDecoder to delay codec initialization until the video frame rate can be estimated. Feedback focuses on thread safety by recommending std::atomic_bool for shared flags, adhering to Chromium style by marking getter methods as const, and improving map access efficiency in the capabilities loading logic.

[datadog-cobalt-youtube]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

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