NQE servicification of UKM page load metrics

Use network quality tracker instead of network quality estimator (NQE)
in UKM page load metrics.

Network quality tracker can provide network service when network
service is enabled as well as when network service is disabled.

Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: Icffe39d2ae493934456ff911290bc50d53efab49
Bug: 819244
Reviewed-on: https://chromium-review.googlesource.com/1177199
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Helen Li <xunjieli@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583873}
5 files changed