ChromeVox spoken feedback reposts unhandled key events

ChromeVox is implemented as a Chrome extension that intercepts events very early on.
The SpokenFeedbackEventRewriter currently passes all key events to the extension when it's enabled.
Any key events that are not handled by the extension are reported back to the rewriter for continued dispatch.
See notes in ash/events/spoken_feedback_event_rewriter* and ash/public/interfaces/event_rewriter_controller.mojom

This reposting of events has two major drawbacks:
1) Added user input latency; key events that aren't handled by ChromeVox are passed around prior to dispatch.
2) Reposted key events may be dispatched out-of-order relative to mouse/etc. events that aren't sent to ChromeVox.

My preferred solution is moving logic from the extension to the low-level rewriter:
In this approach, the rewriter would synchronously determine which events the extension needs to consume (or passively observe?).

There's also a minor related defect that reposted key events are not sent to other EventRewriters.