Add two UMA metrics to track session status when the session go away on path degrading.

Bug: 871407
Change-Id: I7ac4e7370b1aadd2cf9c702a1218abb789f87c29
Reviewed-on: https://chromium-review.googlesource.com/1173507Reviewed-by: Zhongyi Shi <zhongyi@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Renjie Tang <renjietang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583922}

net/quic/quic_chromium_client_session.cc

@@ -2067,6 +2067,12 @@ void QuicChromiumClientSession::OnPathDegrading() {
     net_log_.AddEvent(
         NetLogEventType::QUIC_SESSION_CLIENT_GOAWAY_ON_PATH_DEGRADING);
     NotifyFactoryOfSessionGoingAway();
+    UMA_HISTOGRAM_COUNTS_1M(
+        "Net.QuicSession.ActiveStreamsOnGoAwayAfterPathDegrading",
+        GetNumActiveStreams());
+    UMA_HISTOGRAM_COUNTS_1M(
+        "Net.QuicSession.DrainingStreamsOnGoAwayAfterPathDegrading",
+        GetNumDrainingStreams());
     return;
   }
 

tools/metrics/histograms/histograms.xml

@@ -54487,6 +54487,15 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="Net.QuicSession.ActiveStreamsOnGoAwayAfterPathDegrading"
+    units="Streams">
+  <owner>renjietang@chromium.org</owner>
+  <summary>
+    The number of active streams when the quic session decides to go away on
+    path degrading.
+  </summary>
+</histogram>
+
 <histogram name="Net.QuicSession.AsyncRead" enum="Boolean">
   <owner>rch@chromium.org</owner>
   <summary>
@@ -54725,6 +54734,15 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="Net.QuicSession.DrainingStreamsOnGoAwayAfterPathDegrading"
+    units="Streams">
+  <owner>renjietang@chromium.org</owner>
+  <summary>
+    The number of draining streams when the quic session decides to go away on
+    path degrading.
+  </summary>
+</histogram>
+
 <histogram name="Net.QuicSession.DuplicatePacketsReceived">
   <owner>rch@chromium.org</owner>
   <summary>