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

net/log/file_net_log_observer.h

 // Copyright 2016 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_FILE_NET_LOG_OBSERVER_H_
 #define NET_LOG_FILE_NET_LOG_OBSERVER_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 91 matching lines @@
 
   // Stops observing net_log(). Must be called after StartObservingBounded/
   // StartObservingUnbounded. Should be called before destruction of the
   // FileNetLogObserver and the NetLog, or the NetLog files will be deleted when
   // the observer is destroyed.
   //
   // |callback| will be run on whichever thread StopObserving() was called on
   // once all file writing is complete and the netlog files can be accessed
   // safely.
   //
-  // |url_request_context| is an optional argument used to add additional
-  // network stack state to the log. If the context is non-NULL,
-  // StopObserving() must be called on the context's thread.
-  void StopObserving(URLRequestContext* url_request_context,
+  // |polled_data| is an optional argument used to add additional network stack
+  // state to the log.
+  void StopObserving(std::unique_ptr<base::Value> polled_data,
                      const base::Closure& callback);
 
   // NetLog::ThreadSafeObserver
   void OnAddEntry(const NetLogEntry& entry) override;
 
  private:
   class WriteQueue;
   class FileWriter;
   class BoundedFileWriter;
   class UnboundedFileWriter;
@@ skipping 22 matching lines @@
   // thread is safe because the FileWriter object will be alive until the
   // observer's destruction.
   FileWriter* file_writer_;
 
   DISALLOW_COPY_AND_ASSIGN(FileNetLogObserver);
 };
 
 }  // namespace net
 
 #endif  // NET_LOG_FILE_NET_LOG_OBSERVER_H_