cleanup: Use EventRouter instead of ExtensionSystem::Get->event_router()

chrome/browser/extensions/api/preference/preference_helpers.cc

Index: chrome/browser/extensions/api/preference/preference_helpers.cc
diff --git a/chrome/browser/extensions/api/preference/preference_helpers.cc b/chrome/browser/extensions/api/preference/preference_helpers.cc
index fe55fd719453055d0add78792d275250360102b5..09b00f39ba85ddcbaba8d1650f3b176fa20c0a21 100644
--- a/chrome/browser/extensions/api/preference/preference_helpers.cc
+++ b/chrome/browser/extensions/api/preference/preference_helpers.cc
@@ -89,8 +89,7 @@ void DispatchEventToExtensions(
     APIPermission::ID permission,
     bool incognito,
     const std::string& browser_pref) {
-  EventRouter* router =
-      ExtensionSystem::Get(profile)->event_router();
+  EventRouter* router = EventRouter::Get(profile);
   if (!router || !router->HasEventListener(event_name))
     return;
   ExtensionService* extension_service =