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

[mmenke, 2014/09/03 19:12:10]

nit:  "Trace enable" -> "trace enable" or "TraceLog enable".  Trace isn't a
class name, so should probably not be capitalized

[xunjieli, 2014/09/08 14:08:41]

Done.

+// events to TraceLog if it is enabled.
+class NET_EXPORT TraceNetLogObserver
+    : public NetLog::ThreadSafeObserver,
+      public base::debug::TraceLog::EnabledStateObserver {

[mmenke, 2014/09/03 19:12:10]

Per email comment, EnabledStateObserver is not declared as BASE_EXPORT.  We
should resolve that before landing.  I'm fine with landing with the call to
SetCurrentThreadBlocksMessageLoop, if needed.

[xunjieli, 2014/09/08 14:08:41]

Acknowledged. The deadlock problem has been fixed by Xianzhu. I have removed
SetCurrentThreadBlocksMessageLoop and rebased. I put BASE_EXPORT in the CL where
we added the trace APIs. I will wait for that Cl to land first before commit
this one.

+ 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 already watching for events.
+  // Watches NetLog only when tracing is enabled.
+  void WatchForTraceStart(NetLog* net_log);
+
+  // Stop watching for TraceLog enable and disable events.
+  // If WatchForTraceStart is called, this must be called before
+  // 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_