Avoid using BrowserThread and ContentBrowserClient in NetLogObserver.

content/browser/loader/netlog_observer.h

 // Copyright (c) 2012 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 CONTENT_BROWSER_LOADER_NETLOG_OBSERVER_H_
 #define CONTENT_BROWSER_LOADER_NETLOG_OBSERVER_H_
 
 #include <stdint.h>
 
 #include "base/containers/hash_tables.h"
+#include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/single_thread_task_runner.h"
 #include "content/public/common/resource_devtools_info.h"
 #include "net/log/net_log.h"
 
 namespace net {
 class URLRequest;
 }  // namespace net
 
 namespace content {
 struct ResourceResponse;
 
 // NetLogObserver watches the NetLog event stream and collects the stuff that
 // may be of interest to the client. Currently, this only includes actual
 // HTTP/SPDY headers sent and received over the network.
 //
 // As NetLogObserver shares live data with objects that live on the IO Thread,
 // it must also reside on the IO Thread.  Only OnAddEntry can be called from
 // other threads.
 class NetLogObserver : public net::NetLog::ThreadSafeObserver {
   typedef ResourceDevToolsInfo ResourceInfo;
 
  public:
   // net::NetLog::ThreadSafeObserver implementation:
   void OnAddEntry(const net::NetLog::Entry& entry) override;
 
-  void OnAddURLRequestEntry(const net::NetLog::Entry& entry);
+  // The NetLog instance is passed in via the |net_log| parameter.
+  // A reference to the IO thread task runner is passed via the
+  // |io_thread_runner| parameter.
+  static void Attach(
+      net::NetLog* net_log,
+      scoped_refptr<base::SingleThreadTaskRunner> io_thread_runner);
 
-  static void Attach();
   static void Detach();
 
   // Must be called on the IO thread. May return NULL if no observers
   // are active.
   static NetLogObserver* GetInstance();
   static void PopulateResponseInfo(net::URLRequest*, ResourceResponse*);
 
  private:
   static NetLogObserver* instance_;
 
   NetLogObserver();
   ~NetLogObserver() override;
 
   ResourceInfo* GetResourceInfo(uint32_t id);
 
+  void OnAddURLRequestEntry(const net::NetLog::Entry& entry);
+
   typedef base::hash_map<uint32_t, scoped_refptr<ResourceInfo>>
       RequestToInfoMap;
   RequestToInfoMap request_to_info_;
 
+  // Contains the IO thread task runner instance.
+  static base::LazyInstance<scoped_refptr<base::SingleThreadTaskRunner>>::Leaky
+      io_thread_task_runner_;
+
   DISALLOW_COPY_AND_ASSIGN(NetLogObserver);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_LOADER_NETLOG_OBSERVER_H_