Replace FOR_EACH_OBSERVER in c/b/chromeos with range-based for

chrome/browser/chromeos/system/system_clock.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/system/system_clock.h"
 
 #include <memory>
 
 #include "base/logging.h"
 #include "chrome/browser/chrome_notification_types.h"
@@ skipping 194 matching lines @@
 
 void SystemClock::OnSystemPrefChanged() {
   UpdateClockType();
 }
 
 void SystemClock::UpdateClockType() {
   // This also works for enterprise-managed devices because they never have
   // a local owner.
   if (user_manager::UserManager::Get()->IsCurrentUserOwner())
     SetShouldUse24HourClock(ShouldUse24HourClock());
-  FOR_EACH_OBSERVER(SystemClockObserver, observer_list_,
-                    OnSystemClockChanged(this));
+  for (auto& observer : observer_list_)
+    observer.OnSystemClockChanged(this);
 }
 
 }  // namespace system
 }  // namespace chromeos