Check for network connectivity to decide if the Assistant should run

Previously we checked for network connections, which gave a false
positive if the connected network had no internet connection.

The network connectivity is checked using the (new) CrosNetworkConfig service.

TBR=msarda@chromium.org

Bug: 960956
Change-Id: Id315812b3db1f5445ffdfb95011638e48abafd19
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1643953
Commit-Queue: Jeroen Dhollander <jeroendh@google.com>
Reviewed-by: Tao Wu <wutao@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672240}
14 files changed