Move net-export thread-hopping code into NetLogFileWriter and add IO polled data.

net/log/write_to_file_net_log_observer.h

 // Copyright 2013 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.
 
 #ifndef NET_LOG_WRITE_TO_FILE_NET_LOG_OBSERVER_H_
 #define NET_LOG_WRITE_TO_FILE_NET_LOG_OBSERVER_H_
 
 #include <stdio.h>
 
 #include "base/files/scoped_file.h"
@@ skipping 35 matching lines @@
   // pre-populate the log with information about in-progress events.
   // If the context is non-NULL, this must be called on the context's thread.
   void StartObserving(NetLog* net_log,
                       base::ScopedFILE file,
                       base::Value* constants,
                       URLRequestContext* url_request_context);
 
   // Stops observing net_log().  Must already be watching.  Must be called
   // before destruction of the WriteToFileNetLogObserver and the NetLog.
   //
-  // |url_request_context| is an optional argument used to added additional
-  // network stack state to the log.  If the context is non-NULL, this must be
-  // called on the context's thread.
-  void StopObserving(URLRequestContext* url_request_context);
+  // |polled_data| is an optional argument used to added additional
+  // network stack state to the log.
+  void StopObserving(base::Value* polled_data);
 
   // net::NetLog::ThreadSafeObserver implementation:
   void OnAddEntry(const NetLogEntry& entry) override;
 
  private:
   // ----------------
   // Thread safety
   // ----------------
   //
   // NetLog observers are invoked on arbitrary threads, however are notified of
@@ skipping 14 matching lines @@
 
   // True if OnAddEntry() has been called at least once.
   bool added_events_;
 
   DISALLOW_COPY_AND_ASSIGN(WriteToFileNetLogObserver);
 };
 
 }  // namespace net
 
 #endif  // NET_LOG_WRITE_TO_FILE_NET_LOG_OBSERVER_H_