Set an expiry date for unused histograms (Net.*)

These are histograms that have not been viewed in the last 6 months, but still
report data on the Stable channel. Set these histograms to stop being recorded
for Chrome releases after 2018-08-30. We will file bugs via Monorail (crbug)
reminding owners about the approaching histogram expiry – initially 30 days
prior to expiry, and also with follow-up alerts. The metrics dashboards will
also display a warning for anyone viewing a soon-to-expire histogram.

Owners and/or users of these histograms: Please comment on this CL if you think
that any affected histogram should not have an expiry date set! This should be
uncommon.

Otherwise, there are a few options going forward:
  * If the histogram is no longer needed, please send a follow-up CL to delete
    the recording code and to mark the histogram as <obsolete>. (You can also
    remove the expiry date in the same CL.)
  * If you want to set a different expiry date, please send a follow-up CL to do
    so.
  * If neither of the above apply, then keep an eye out for Monorail bugs as the
    histogram expiry date approaches.
For more info on how unused histograms are identified, see
https://goto.google.com/uma-unused-histograms-cleanup

Bug: 850539
Change-Id: I84a9b876102f223e46da4314a5b616d245a46358
Reviewed-on: https://chromium-review.googlesource.com/1126319
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Ryan Hamilton <rch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573510}

tools/metrics/histograms/histograms.xml

@@ -47870,7 +47870,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.AlternativeServiceServers.MoreOrEqualCacheEntries">
+<histogram name="Net.AlternativeServiceServers.MoreOrEqualCacheEntries"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The difference between the size of alternative service mappings in cache and
@@ -51044,7 +51045,7 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Net.HttpServerProperties.UpdatePrefs"
-    enum="HttpServerPropertiesUpdatePrefsLocation">
+    enum="HttpServerPropertiesUpdatePrefsLocation" expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The location in http_server_properties_manager.cc where UpdatePrefs was
@@ -52495,7 +52496,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicClientHelloServerConfig.InvalidDuration" units="ms">
+<histogram name="Net.QuicClientHelloServerConfig.InvalidDuration" units="ms"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The time since expiration of server config when we sent inchoate ClientHello
@@ -52535,7 +52537,7 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Net.QuicCryptoClientConfig.PopulatedFromCanonicalConfig"
-    enum="BooleanPopulated">
+    enum="BooleanPopulated" expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The number of times CryptoClientConfig's CachedState is populated from
@@ -52647,7 +52649,7 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Net.QuicInchoateClientHelloReason"
-    enum="QuicServerConfigState">
+    enum="QuicServerConfigState" expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The reason (the state of the server config) for sending inchoate ClientHello
@@ -52702,14 +52704,15 @@ uploading your change for review.
   <summary>The number of times ServerConfigUpdateMessages ignored.</summary>
 </histogram>
 
-<histogram name="Net.QuicNumStreamFramesInPacket">
+<histogram name="Net.QuicNumStreamFramesInPacket" expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The number of stream frames bundled within a received packet.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicNumStreamFramesPerStreamInPacket">
+<histogram name="Net.QuicNumStreamFramesPerStreamInPacket"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The number of stream frames per stream ID within a received packet.
@@ -52888,7 +52891,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.ClientSideMtu" units="bytes">
+<histogram name="Net.QuicSession.ClientSideMtu" units="bytes"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The final maximum packet size of the connection used by the client before
@@ -52903,7 +52907,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.ClosedDuringInitializeSession" enum="Boolean">
+<histogram name="Net.QuicSession.ClosedDuringInitializeSession" enum="Boolean"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
      True if the QUIC session is closed during the call to InitializeSession,
@@ -52937,7 +52942,7 @@ uploading your change for review.
 
 <histogram
     name="Net.QuicSession.ConnectionClose.HandshakeFailureBlackHole.QuicError"
-    enum="QuicErrorCodes">
+    enum="QuicErrorCodes" expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The QUIC error which caused a QUIC connection to be closed before the
@@ -53067,7 +53072,7 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Net.QuicSession.CookieSentToAccountsOverChannelId"
-    enum="BooleanUsage">
+    enum="BooleanUsage" expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     Logs whether channel ID was used when a cookie is sent over QUIC to
@@ -53187,7 +53192,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.IncorrectConnectionIDsReceived">
+<histogram name="Net.QuicSession.IncorrectConnectionIDsReceived"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The number packets recevied by a QuicSession with an incorrect connection id
@@ -53253,7 +53259,7 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.MtuProbesSent">
+<histogram name="Net.QuicSession.MtuProbesSent" expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The number of MTU probes sent by the client during the session.  Logged when
@@ -53312,7 +53318,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.OutOfOrderLargePacketsReceived">
+<histogram name="Net.QuicSession.OutOfOrderLargePacketsReceived"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The number of times the current received packet had a lower sequence number
@@ -53510,14 +53517,15 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.RejectHasProof" enum="Boolean">
+<histogram name="Net.QuicSession.RejectHasProof" enum="Boolean"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     True if the QUIC REJ message received from the server contains a proof.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.RejectLength">
+<histogram name="Net.QuicSession.RejectLength" expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The length in bytes of a QUIC REJ message received from the server.
@@ -53576,7 +53584,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.ServerSideMtu" units="bytes">
+<histogram name="Net.QuicSession.ServerSideMtu" units="bytes"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The largest packet which the client received from the server during the
@@ -53654,7 +53663,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.TimedOutWithOpenStreams.ConsecutiveRTOCount">
+<histogram name="Net.QuicSession.TimedOutWithOpenStreams.ConsecutiveRTOCount"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     If a QUIC connection timed out with open streams, this contains a count of
@@ -53662,7 +53672,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.TimedOutWithOpenStreams.ConsecutiveTLPCount">
+<histogram name="Net.QuicSession.TimedOutWithOpenStreams.ConsecutiveTLPCount"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     If a QUIC connection timed out with open streams, this contains a count of
@@ -53670,7 +53681,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.TimedOutWithOpenStreams.HasUnackedPackets">
+<histogram name="Net.QuicSession.TimedOutWithOpenStreams.HasUnackedPackets"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     If a QUIC connection timed out with open streams, this will be true when the
@@ -53678,7 +53690,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.TimedOutWithOpenStreams.LocalPort">
+<histogram name="Net.QuicSession.TimedOutWithOpenStreams.LocalPort"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     If a QUIC connection timed out locally with open streams, this contains the
@@ -53696,7 +53709,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram name="Net.QuicSession.TooManyOpenStreams" enum="BooleanTooMany">
+<histogram name="Net.QuicSession.TooManyOpenStreams" enum="BooleanTooMany"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     True if more than 100 streams are open when a new stream is activated.
@@ -53719,7 +53733,8 @@ uploading your change for review.
   <summary>The number of truncated ACK frames sent.</summary>
 </histogram>
 
-<histogram name="Net.QuicSession.UndecryptablePacketsReceived">
+<histogram name="Net.QuicSession.UndecryptablePacketsReceived"
+    expires_after="2018-08-30">
   <owner>rch@chromium.org</owner>
   <summary>
     The number of undecryptable packets recevied by a QuicSession when the