Fix WeakPtrFactory member ordering in chrome/browser/sync

Changing the initialization order of WeakPtrFactory such that all
member variables should appear before the WeakPtrFactory to ensure
that any WeakPtrs to Controller are invalidated before its members
variable's destructors are executed, rendering them invalid.

BUG=303818

Review URL: https://codereview.chromium.org/591993002

Cr-Commit-Position: refs/heads/master@{#296005}

chrome/browser/sync/sessions/notification_service_sessions_router.h

@@ -59,11 +59,12 @@ class NotificationServiceSessionsRouter
   content::NotificationRegistrar registrar_;
   Profile* const profile_;
   syncer::SyncableService::StartSyncFlare flare_;
-  base::WeakPtrFactory<NotificationServiceSessionsRouter> weak_ptr_factory_;
 
   scoped_ptr<base::CallbackList<void(const std::set<GURL>&)>::Subscription>
       favicon_changed_subscription_;
 
+  base::WeakPtrFactory<NotificationServiceSessionsRouter> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(NotificationServiceSessionsRouter);
 };