Move active network state tracking to ash::TrayNetworkStateObserver

This CL moves active network state tracking from ActiveNetworkIcon to
TrayNetworkStateObserver in preparation for other Ash UI (e.g. the
network feature pods) to uses the same cached states.

Bug: 862420
Change-Id: I742bb56bfcd54df196f5e4078b85f09c51a809cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1622745
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661842}
8 files changed