Get rid of sync_preferences::SyncedPrefObserver inheritance.

chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl_unittest.cc

Index: chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl_unittest.cc
diff --git a/chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl_unittest.cc b/chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl_unittest.cc
index 3276ab1ddf0dc1a190ad981b5151574dd1f1b68f..7015f5bab8c71255bd8f5216518b58a554b3fd65 100644
--- a/chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl_unittest.cc
+++ b/chrome/browser/ui/ash/launcher/chrome_launcher_controller_impl_unittest.cc
@@ -832,8 +832,6 @@ class ChromeLauncherControllerImplTest : public BrowserWithTestWindowTest {
   void EnableArc(bool enable) {
     enable ? arc_test_.arc_session_manager()->EnableArc()
            : arc_test_.arc_session_manager()->DisableArc();
-    arc_test_.arc_session_manager()->OnSyncedPrefChanged(prefs::kArcEnabled,
-                                                         false);
     base::RunLoop().RunUntilIdle();
   }