Introduces the notion of a "delegated source list" and corresponding
controller. This is used by desktop capturers (currently just the
PipeWire capturer), who control selecting the source through their own
(often system-level) UI, rather than returning a source list with all
available options that can then be selected by the embedder.
Adds a method to get the controller which serves to also tell embedders
if the capturer makes use of a delegated source list. The controller
currently allows the embedder to request that the delegated source list
be shown or hidden, and will in the future be used to expose events
from the source list (e.g. selection, dismissal, error).
Bug: chromium:1351572
Change-Id: Ie1d36ed654013f59b8d9095deef01a4705fd5bde
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/272621
Reviewed-by: Mark Foltz <mfoltz@chromium.org>
Commit-Queue: Alexander Cooper <alcooper@chromium.org>
Cr-Commit-Position: refs/heads/main@{#37956}
fbea8c5196