tot chrome with chrome://flags #enumerate-audio-devices flag enabled.

What steps will reproduce the problem?
1. Browse to https://webrtc.github.io/samples/src/content/getusermedia/source/
2. Select an available input source
3. Select an output destination

The audio from input source should be routed to selected output destination. However, it is routed to chromeos system UI selected output destination only.

Current status:
Let us plan this bug for M-57 for now.
The input pinning stream is landed in M-54 with #enumerate-audio-devices flag disabled.
M-55 may still need this flag merged.
Decide later for M-56.