SupervisedUserNavigationThrottle: create only for supervised profiles

chrome/browser/supervised_user/supervised_user_url_filter.h

Index: chrome/browser/supervised_user/supervised_user_url_filter.h
diff --git a/chrome/browser/supervised_user/supervised_user_url_filter.h b/chrome/browser/supervised_user/supervised_user_url_filter.h
index e7fb96ef2e16c26b98a4f25184fe0919da81da00..3e3d87da80cac86824dbc96c535efe48781d6801 100644
--- a/chrome/browser/supervised_user/supervised_user_url_filter.h
+++ b/chrome/browser/supervised_user/supervised_user_url_filter.h
@@ -57,7 +57,11 @@ class SupervisedUserURLFilter : public base::NonThreadSafe {
 
   class Observer {
    public:
+    // Called whenever the whitelists are updated. This does *not* include
+    // SetManualHosts/SetManualURLs.
     virtual void OnSiteListUpdated() = 0;
+    // Called whenever a check started via
+    // GetFilteringBehaviorForURLWithAsyncChecks completes.
     virtual void OnURLChecked(
         const GURL& url,
         FilteringBehavior behavior,