See the design doc[1] for further info. We would like to redesign
the places observer system to be more performant and more friendly
to consume. WebIDL was recommended as it simplifies creating simple
dictionary payloads while allowing dynamic typing with `any`.
There were some difficulties with WebIDL though, most of which
revolved around allowing consumers to be weakly referenced, from
both C++ and JS. The simplest solution I could come up with was to
create a simple native interface for the C++ case, and a WebIDL
wrapper for a JS callback in the JS case. Suggestions for simpler
alternatives are very welcome though.
[1] https://docs.google.com/document/d/1G45vfd6RXFXwNz7i4FV40lDCU0ao-JX_bZdgJV4tLjk/edit?usp=sharing
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