All replays being deleted without warning

[chrahunt]

There have been several reports from users of all of their replays disappearing. This issue tracks progress and individual circumstances to try and find a root cause.

Initially I thought this was due to normal eviction by the browser when the user's disk gets close to full, but per the comment here, extensions with the unlimitedStorage permission (like ours) should not have any storage evicted under any circumstances.

[zmunro]

@chrahunt I can try to look into this. Would you be willing to help me find where the files are stored locally?