Replacing observer interface with polling for pending probe clusters.
The purpose is to make it easier to reason about and control side
effects and to prepare for a similar change in the network controller
interface.
Bug: webrtc:8415
Change-Id: I8101cfda22e640a8e0fa75f3f6e63876db826a89
Reviewed-on: https://webrtc-review.googlesource.com/66881
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22775}
f2e3e7a25a