fun saveState(): Map<String, Any> (source)
Overrides EngineSession.saveState
GeckoView provides a String representing the entire session state. We store this String using a single Map entry with key GECKO_STATE_KEY.
See https://bugzilla.mozilla.org/show_bug.cgi?id=1441810 for discussion on sync vs. async, where a decision was made that callers should provide synchronous wrappers, if needed. In case we're asking for the state when persisting, a separate (independent) thread is used so we're not blocking anything else. In case of calling this method from onPause or similar, we also want a synchronous response.