Fix a flaky QUIC end_to_end_test when the socket was suddenly unwritable

net/quic/quic_connection.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/quic/quic_connection.h"
 
 #include <string.h>
 #include <sys/types.h>
 #include <algorithm>
 #include <iterator>
@@ skipping 1272 matching lines @@
   // We should serialize handshake packets immediately to ensure that they
   // end up sent at the right encryption level.
   if (handshake == IS_HANDSHAKE) {
     return true;
   }
 
   return CanWrite(retransmittable);
 }
 
 bool QuicConnection::CanWrite(HasRetransmittableData retransmittable) {
+  if (!connected_) {
+    return false;
+  }
+
   if (writer_->IsWriteBlocked()) {
     visitor_->OnWriteBlocked();
     return false;
   }
 
   QuicTime now = clock_->Now();
   QuicTime::Delta delay = sent_packet_manager_.TimeUntilSend(
       now, retransmittable);
   if (delay.IsInfinite()) {
     send_alarm_->Cancel();
@@ skipping 703 matching lines @@
   }
   for (size_t i = 0; i < retransmittable_frames->frames().size(); ++i) {
     if (retransmittable_frames->frames()[i].type == CONNECTION_CLOSE_FRAME) {
       return true;
     }
   }
   return false;
 }
 
 }  // namespace net