Intent to prototype and ship: Compression Streams

[Kagami Rosylight]

As of March 25 (past, yes 😅) I intend to prototype and ship Compression Streams. This feature allows JavaScript to compress and decompress some industry standard compression formats, namely deflate/deflate-raw/gzip.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1823619
Specification: https://wicg.github.io/compression/
Standards body: Still in WICG yet and it's not clear to which body it will go. See https://github.com/WICG/compression/issues/32 for details.
Platform coverage: All
Preference: dom.compression_streams.enabled (on by default)
Mozilla standard position: positive. https://mozilla.github.io/standards-positions/#compression-streams
Other browsers: Shipped in Chrome 80, shipping in Safari 16.4 (still in beta)
Web platform tests: https://wpt.fyi/results/compression (All green!)

How stable is the spec: There have been minimal changes with no visible behavior change since 2019/2020.
Security & privacy concerns: This uses an external library named zlib. While this library is old, mature, and being used by nearly everyone including multiple existing components in Gecko, extra fuzzing will still be helpful. The same library is used in Blink and WebKit to implement this feature. For privacy, this does not expose any system configuration. See also https://wicg.github.io/compression/#privacy-security.
Web developer use cases: Zip files can be created without depending on JS/wasm compression libraries, for example.
Example: https://wicg.github.io/compression/#examples