Update NetLog to be thread safe.

chrome/browser/net/load_timing_observer.cc

Index: chrome/browser/net/load_timing_observer.cc
===================================================================
--- chrome/browser/net/load_timing_observer.cc	(revision 65207)
+++ chrome/browser/net/load_timing_observer.cc	(working copy)
@@ -44,7 +44,7 @@
       (time_ticks - record->base_ticks).InMillisecondsRoundedUp());
 }
 
-}
+}  // namespace
 
 LoadTimingObserver::URLRequestRecord::URLRequestRecord()
     : connect_job_id(net::NetLog::Source::kInvalidId),
@@ -73,6 +73,9 @@
                                     const net::NetLog::Source& source,
                                     net::NetLog::EventPhase phase,
                                     net::NetLog::EventParameters* params) {
+  // The events that the Observer is interested in only occur on the IO thread.
+  if (!BrowserThread::CurrentlyOn(BrowserThread::IO))
+    return;
   if (source.type == net::NetLog::SOURCE_URL_REQUEST)
     OnAddURLRequestEntry(type, time, source, phase, params);
   else if (source.type == net::NetLog::SOURCE_CONNECT_JOB)