Use NESTABLE_ASYNC APIs to get NetLog data into Tracing

net/base/trace_net_log_observer.h

+// Copyright 2014 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_BASE_TRACE_NET_LOG_OBSERVER_H_
+#define NET_BASE_TRACE_NET_LOG_OBSERVER_H_
+
+#include "base/debug/trace_event_impl.h"
+#include "base/macros.h"
+#include "net/base/net_export.h"
+#include "net/base/net_log.h"
+
+namespace net {
+
+// TraceNetLogObserver watches for Trace enable, and sends NetLog
+// events to TraceLog if it is enabled.
+class NET_EXPORT TraceNetLogObserver
+    : public NetLog::ThreadSafeObserver,
+      public base::debug::TraceLog::EnabledStateObserver {
+ public:
+  TraceNetLogObserver();
+  virtual ~TraceNetLogObserver();
+
+  // net::NetLog::ThreadSafeObserver implementation:
+  virtual void OnAddEntry(const NetLog::Entry& entry) OVERRIDE;
+
+  // Start to watch for TraceLog enable and disable events.
+  // This can't be called if TraceNetLogObserver is currently watching.

[mmenke, 2014/09/02 21:28:59]

Maybe:

Start to watch for TraceLog enable and disable events.
This can't be called if already watching for events.
Watches NetLog only when tracing is enabled.

[xunjieli, 2014/09/02 23:57:17]

Done.

+  void WatchForTraceStart(NetLog* net_log);
+
+  // Stop watching for TraceLog enable and disable events.
+  // If WatchForTraceStart is called, this should be called before

[mmenke, 2014/09/02 21:28:59]

should -> must

[xunjieli, 2014/09/02 23:57:17]

Done.

+  // TraceNetLogObserver is destroyed.
+  void StopWatchForTraceStart();
+
+  // base::debug::TraceLog::EnabledStateChangedObserver implementation:
+  virtual void OnTraceLogEnabled() OVERRIDE;
+  virtual void OnTraceLogDisabled() OVERRIDE;
+
+ private:
+  NetLog* net_log_to_watch_;
+
+  DISALLOW_COPY_AND_ASSIGN(TraceNetLogObserver);
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_TRACE_NET_LOG_OBSERVER_H_