Remove the last usages of PrefObserver outside of Prefs.

chrome/browser/net/chrome_network_delegate.cc

Index: chrome/browser/net/chrome_network_delegate.cc
diff --git a/chrome/browser/net/chrome_network_delegate.cc b/chrome/browser/net/chrome_network_delegate.cc
index 60022e98ecb34cec7f824e781f1fd1a92f46814b..710c2f8a8bce813901f1aecdbe69d643669d934b 100644
--- a/chrome/browser/net/chrome_network_delegate.cc
+++ b/chrome/browser/net/chrome_network_delegate.cc
@@ -303,16 +303,16 @@ void ChromeNetworkDelegate::InitializePrefsOnUIThread(
     BooleanPrefMember* force_google_safe_search,
     PrefService* pref_service) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  enable_referrers->Init(prefs::kEnableReferrers, pref_service, NULL);
+  enable_referrers->Init(prefs::kEnableReferrers, pref_service);
   enable_referrers->MoveToThread(
       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO));
   if (enable_do_not_track) {
-    enable_do_not_track->Init(prefs::kEnableDoNotTrack, pref_service, NULL);
+    enable_do_not_track->Init(prefs::kEnableDoNotTrack, pref_service);
     enable_do_not_track->MoveToThread(
         BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO));
   }
   if (force_google_safe_search) {
-    force_google_safe_search->Init(prefs::kForceSafeSearch, pref_service, NULL);
+    force_google_safe_search->Init(prefs::kForceSafeSearch, pref_service);
     force_google_safe_search->MoveToThread(
         BrowserThread::GetMessageLoopProxyForThread(BrowserThread::IO));
   }