Update NetLog to be thread safe.

chrome/browser/net/net_log_logger.cc

 // Copyright (c) 2010 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 "chrome/browser/net/net_log_logger.h"
 
 #include "base/json/json_writer.h"
 #include "base/values.h"
 
-NetLogLogger::NetLogLogger() : Observer(net::NetLog::LOG_ALL_BUT_BYTES) {}
+NetLogLogger::NetLogLogger()
+    : ThreadSafeObserver(net::NetLog::LOG_ALL_BUT_BYTES) {
+}
 
 NetLogLogger::~NetLogLogger() {}
 
 void NetLogLogger::OnAddEntry(net::NetLog::EventType type,
                               const base::TimeTicks& time,
                               const net::NetLog::Source& source,
                               net::NetLog::EventPhase phase,
                               net::NetLog::EventParameters* params) {
   scoped_ptr<Value> value(net::NetLog::EntryToDictionaryValue(type, time,
                                                               source, phase,
                                                               params, true));
   std::string json;
   base::JSONWriter::Write(value.get(), true, &json);
   VLOG(1) << json;
 }