Quic: Add histogram that records whether key update was supported by each connection.

Bug: b/170619368
Change-Id: I2f882da7205380ecceb471c6fec553a27e69421d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495710
Commit-Queue: Matt Mueller <mattm@chromium.org>
Reviewed-by: David Schinazi <dschinazi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821100}

net/quic/quic_chromium_client_session.cc

@@ -1870,6 +1870,28 @@ void QuicChromiumClientSession::OnConnectionClosed(
         "Net.QuicSession.ConnectionDuration",
         tick_clock_->NowTicks() - connect_timing_.connect_end);
     UMA_HISTOGRAM_COUNTS_100("Net.QuicSession.NumMigrations", num_migrations_);
+    // These values are persisted to logs. Entries should not be renumbered
+    // and numeric values should never be reused.
+    enum class KeyUpdateSupported {
+      kInvalid = 0,
+      kUnsupported = 1,
+      kSupported = 2,
+      kSupportedLocallyOnly = 3,
+      kSupportedRemotelyOnly = 4,
+      kMaxValue = kSupportedRemotelyOnly,
+    };
+    KeyUpdateSupported key_update_supported = KeyUpdateSupported::kInvalid;
+    if (config()->KeyUpdateSupportedForConnection()) {
+      key_update_supported = KeyUpdateSupported::kSupported;
+    } else if (config()->KeyUpdateSupportedLocally()) {
+      key_update_supported = KeyUpdateSupported::kSupportedLocallyOnly;
+    } else if (config()->KeyUpdateSupportedRemotely()) {
+      key_update_supported = KeyUpdateSupported::kSupportedRemotelyOnly;
+    } else {
+      key_update_supported = KeyUpdateSupported::kUnsupported;
+    }
+    base::UmaHistogramEnumeration("Net.QuicSession.KeyUpdate.Supported",
+                                  key_update_supported);
     if (config()->KeyUpdateSupportedForConnection()) {
       base::UmaHistogramCounts100("Net.QuicSession.KeyUpdate.PerConnection2",
                                   connection()->GetStats().key_update_count);

tools/metrics/histograms/enums.xml

@@ -61376,6 +61376,14 @@ https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_2.7.1.pdf
   <int value="3" label="kFailedNonInitial"/>
 </enum>
 
+<enum name="QuicKeyUpdateSupported">
+  <int value="0" label="kInvalid"/>
+  <int value="1" label="kUnsupported"/>
+  <int value="2" label="kSupported"/>
+  <int value="3" label="kSupportedLocallyOnly"/>
+  <int value="4" label="kSupportedRemotelyOnly"/>
+</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

@@ -2976,6 +2976,17 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </token>
 </histogram>
 
+<histogram name="Net.QuicSession.KeyUpdate.Supported"
+    enum="QuicKeyUpdateSupported" expires_after="2021-05-11">
+  <owner>mattm@chromium.org</owner>
+  <owner>src/net/quic/OWNERS</owner>
+  <summary>
+    Whether key update was supported by either or both sides of the connection,
+    recorded on connection close. Only logged for connections which reached the
+    1-RTT level.
+  </summary>
+</histogram>
+
 <histogram
     name="Net.QuicSession.LastInFlightPacketSentTimeFromHandshakeCompletionWithPublicReset"
     units="ms" expires_after="2021-05-11">