Add a new histogram: Net.QuicSession.OutOfOrderGapReceived

The number of missing packets between the current received packet and the
previously largest received packet sequence number, when the current
received packet had a lower sequence number than the previously received
packet sequence number.

Review URL: https://chromiumcodereview.appspot.com/23451015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221955 0039d316-1c4b-4281-b951-d872f2087c98

net/quic/quic_connection_logger.cc

@@ -301,6 +301,9 @@ void QuicConnectionLogger::OnPacketHeader(const QuicPacketHeader& header) {
   }
   if (header.packet_sequence_number < last_received_packet_sequence_number_) {
     ++out_of_order_recieved_packet_count_;
+    UMA_HISTOGRAM_COUNTS("Net.QuicSession.OutOfOrderGapReceived",
+                         last_received_packet_sequence_number_ -
+                             header.packet_sequence_number);
   }
   last_received_packet_sequence_number_ = header.packet_sequence_number;
 }

tools/metrics/histograms/histograms.xml

@@ -7808,10 +7808,19 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Net.QuicSession.OutOfOrderGapReceived">
+  <summary>
+    The number of missing packets between the current received packet and the
+    previously largest received packet sequence number, when the current
+    received packet had a lower sequence number than the previously received
+    packet sequence number.
+  </summary>
+</histogram>
+
 <histogram name="Net.QuicSession.OutOfOrderPacketsReceived">
   <summary>
-    The number of times packets the current received packet had a lower sequence
-    number than the previously received packet sequence number.
+    The number of times the current received packet had a lower sequence number
+    than the previously received packet sequence number.
   </summary>
 </histogram>