This is needed to support the HTMLMediaElements seek functionality.
Unless I'm mistaken, it's already supported: https://github.com/servo/servo/blob/c3c68983b7c10731ce13f055a9d778e9b8b1bd94/components/net/http_cache.rs#L366
I think this may only require adding APIs for fetching subsets of data that the HTML media element code can use. I don't think there's anything at the network layer that we do not support yet.
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Unless I'm mistaken, it's already supported: https://github.com/servo/servo/blob/c3c68983b7c10731ce13f055a9d778e9b8b1bd94/components/net/http_cache.rs#L366