Fix crash in NQE: Replace DCHECK by an if-conditional

net/nqe/network_quality_estimator.cc

 // Copyright 2015 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/nqe/network_quality_estimator.h"
 
 #include <algorithm>
 #include <cmath>
 #include <limits>
 #include <utility>
@@ skipping 783 matching lines @@
   if (RandDouble() >= correlation_uma_logging_probability_)
     return;
 
   if (request.response_info().was_cached ||
       !request.response_info().network_accessed) {
     return;
   }
 
   LoadTimingInfo load_timing_info;
   request.GetLoadTimingInfo(&load_timing_info);
-  DCHECK(!load_timing_info.send_start.is_null() &&
-         !load_timing_info.receive_headers_end.is_null());
+  // If the load timing info is unavailable, it probably means that the request
+  // did not go over the network.
+  if (load_timing_info.send_start.is_null() ||
+      load_timing_info.receive_headers_end.is_null()) {
+    return;
+  }
 
   // Record UMA only for successful requests that have completed.
   if (!request.status().is_success() || request.status().is_io_pending())
     return;
   if (request.GetResponseCode() != HTTP_OK)
     return;
   if (load_timing_info.receive_headers_end < last_main_frame_request_)
     return;
 
   const base::TimeTicks now = tick_clock_->NowTicks();
@@ skipping 851 matching lines @@
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK_NE(EFFECTIVE_CONNECTION_TYPE_LAST, effective_connection_type_);
 
   // TODO(tbansal): Add hysteresis in the notification.
   FOR_EACH_OBSERVER(
       EffectiveConnectionTypeObserver, effective_connection_type_observer_list_,
       OnEffectiveConnectionTypeChanged(effective_connection_type_));
 }
 
 }  // namespace net