Quic: Add histogram for key update reason.

Bug: b/170619368
Change-Id: I9ff06c3ef7dee571936dee89ab5e45c64163b1ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2488906Reviewed-by: David Schinazi <dschinazi@chromium.org>
Commit-Queue: Matt Mueller <mattm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820370}

net/quic/quic_chromium_client_session.cc

@@ -2504,6 +2504,8 @@ void QuicChromiumClientSession::OnKeyUpdate(quic::KeyUpdateReason reason) {
   net_log_.AddEventWithStringParams(NetLogEventType::QUIC_SESSION_KEY_UPDATE,
                                     "reason",
                                     quic::KeyUpdateReasonString(reason));
+
+  base::UmaHistogramEnumeration("Net.QuicSession.KeyUpdate.Reason", reason);
 }
 
 void QuicChromiumClientSession::OnProofValid(

tools/metrics/histograms/enums.xml

@@ -61312,6 +61312,15 @@ https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_2.7.1.pdf
   <int value="13668" label="kUnitConversionResult"/>
 </enum>
 
+<enum name="QuicKeyUpdateReason">
+  <int value="0" label="kInvalid"/>
+  <int value="1" label="kRemote"/>
+  <int value="2" label="kLocalForTests"/>
+  <int value="3" label="kLocalForInteropRunner"/>
+  <int value="4" label="kLocalAeadConfidentialityLimit"/>
+  <int value="5" label="kLocalKeyUpdateLimitOverride"/>
+</enum>
+
 <enum name="QuickofficeErrorTypes">
   <int value="0" label="doc uncaught js exception"/>
   <int value="1" label="docx uncaught js exception"/>

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

@@ -2952,6 +2952,13 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="Net.QuicSession.KeyUpdate.Reason" enum="QuicKeyUpdateReason"
+    expires_after="2021-05-11">
+  <owner>mattm@chromium.org</owner>
+  <owner>src/net/quic/OWNERS</owner>
+  <summary>The reason why each key update occured.</summary>
+</histogram>
+
 <histogram
     name="Net.QuicSession.LastInFlightPacketSentTimeFromHandshakeCompletionWithPublicReset"
     units="ms" expires_after="2021-05-11">