Avoid using BrowserThread and ContentBrowserClient in NetLogObserver.

content/browser/loader/netlog_observer.h

Index: content/browser/loader/netlog_observer.h
diff --git a/content/browser/loader/netlog_observer.h b/content/browser/loader/netlog_observer.h
index 330a502e50afd7643ac8a5acb1e2d22f858d3c59..33a83807d1c684033a198773ede9449bdb6f3494 100644
--- a/content/browser/loader/netlog_observer.h
+++ b/content/browser/loader/netlog_observer.h
@@ -8,8 +8,10 @@
 #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"
 
@@ -34,9 +36,13 @@ class NetLogObserver : public net::NetLog::ThreadSafeObserver {
   // 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
@@ -52,10 +58,16 @@ class NetLogObserver : public net::NetLog::ThreadSafeObserver {
 
   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);
 };