Update NetLog to be thread safe.

net/base/net_log.h

Index: net/base/net_log.h
===================================================================
--- net/base/net_log.h	(revision 65207)
+++ net/base/net_log.h	(working copy)
@@ -29,12 +29,9 @@
 // is usually accessed through a BoundNetLog, which will always pass in a
 // specific source ID.
 //
-// Note that NetLog is NOT THREADSAFE.
-//
 // ******** The NetLog (and associated logging) is a work in progress ********
 //
 // TODO(eroman): Remove the 'const' qualitifer from the BoundNetLog methods.
-// TODO(eroman): Make the DNS jobs emit into the NetLog.
 // TODO(eroman): Start a new Source each time URLRequest redirects
 //               (simpler to reason about each as a separate entity).
 
@@ -81,7 +78,7 @@
   // Base class for associating additional parameters with an event. Log
   // observers need to know what specific derivations of EventParameters a
   // particular EventType uses, in order to get at the individual components.
-  class EventParameters : public base::RefCounted<EventParameters> {
+  class EventParameters : public base::RefCountedThreadSafe<EventParameters> {
    public:
     EventParameters() {}
     virtual ~EventParameters() {}