QUIC - Added a histogram to track number of times session_ is null when

net/quic/quic_http_stream.cc

Index: net/quic/quic_http_stream.cc
diff --git a/net/quic/quic_http_stream.cc b/net/quic/quic_http_stream.cc
index 78b793cbcaf3c53b91062a261c92ab3afa7bdba0..bdc0976c575f798ea17923c83bc318be0e616dbe 100644
--- a/net/quic/quic_http_stream.cc
+++ b/net/quic/quic_http_stream.cc
@@ -175,9 +175,13 @@ int QuicHttpStream::InitializeStream(const HttpRequestInfo* request_info,
 }
 
 int QuicHttpStream::DoStreamRequest() {
-  if (session_.get() == nullptr) {
-    // TODO(rtenneti) Bug: b/28676259 - a temporary fix until we find out why
-    // |session_| could be a nullptr.
+  // TODO(rtenneti) Bug: b/28676259 - a temporary fix until we find out why
+  // |session_| could be a nullptr. Delete |null_session| check and histogram if
+  // session is never a nullptr.
+  bool null_session = session_ == nullptr;
+  if (null_session) {
+    UMA_HISTOGRAM_BOOLEAN("Net.QuicHttpStream::DoStreamRequest.NullSession",
+                          null_session);
     return was_handshake_confirmed_ ? ERR_CONNECTION_CLOSED
                                     : ERR_QUIC_HANDSHAKE_FAILED;
   }