Enable active service refreshing for ServiceWatcherImpl

Actively refresh DNS-SD services if they need active refreshing.

What's changed:
- ServiceDiscoveryClient treats both PTR and SRV records as sources of truth regarding a service's existence
- If a service watcher is actively refreshing its record, set each SRV record for a service it finds to actively refresh periodically.
- If a service watcher is actively refreshing its records, query for an SRV record when the service is discovered

BUG=336883

Review URL: https://codereview.chromium.org/145493008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250646 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250646
Automated Commit: Committing new LKGM version 5467.0.0 for chromeos.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250647 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250647