Add QUIC owners to protocol_page_load_metrics_observer.cc

Quite frequently, QUIC folks update versions and need to find a PLM
reviewer. Just let them review these trivial changes themselves.

Bug: None
Change-Id: I9e6e0c824f515e921fb117b05cbff0bfa30b9ecf
Reviewed-on: https://chromium-review.googlesource.com/c/1458799Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630052}

chrome/browser/page_load_metrics/observers/OWNERS

+# For QUIC version changes in ConnectionInfo switch statmenets.
+per-file protocol_page_load_metrics_observer.cc=file://net/quic/OWNERS