Remove expiration of Net.DNS_Resolutoin_And_TCP_Connection_Latency2

This is a core net/ performance metric, and is needed to help
investigate any significant change time URLRequests take to complete.

Bug: 1088996
Change-Id: Ide5f2c0f3f592ce67ad1563fcacbea64fc8b5f16
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2424256Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Commit-Queue: Matt Menke <mmenke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812108}

tools/metrics/histograms/histograms_xml/net/histograms.xml

@@ -1219,7 +1219,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Net.DNS_Resolution_And_TCP_Connection_Latency2" units="ms"
-    expires_after="M85">
+    expires_after="never">
+<!-- expires-never: Core network stack health metric -->
+
   <owner>mmenke@chromium.org</owner>
   <summary>
     The time measured before starting DNS lookup until after the connection is