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

chrome/browser/chromeos/mobile/mobile_activator.cc

Index: chrome/browser/chromeos/mobile/mobile_activator.cc
diff --git a/chrome/browser/chromeos/mobile/mobile_activator.cc b/chrome/browser/chromeos/mobile/mobile_activator.cc
index 32b179b7cdf08707cf6e702d6408c26557cddfd8..58a861375e9d3ecf1d0c0071962686de9ee0c012 100644
--- a/chrome/browser/chromeos/mobile/mobile_activator.cc
+++ b/chrome/browser/chromeos/mobile/mobile_activator.cc
@@ -998,8 +998,8 @@ void MobileActivator::ChangeState(const NetworkState* network,
   state_ = new_state;
 
   // Signal to observers layer that the state is changing.
-  FOR_EACH_OBSERVER(Observer, observers_,
-      OnActivationStateChanged(network, state_, error_description));
+  for (auto& observer : observers_)
+    observer.OnActivationStateChanged(network, state_, error_description);
 
   // Pick action that should happen on entering the new state.
   switch (new_state) {