Added usage of ScreenContext in EulaScreen.

components/login/screens/screen_context.cc

Index: components/login/screens/screen_context.cc
diff --git a/components/login/screens/screen_context.cc b/components/login/screens/screen_context.cc
index 5324164ee6af6283062e8bd79fd44a70c6ebd71c..71ffdf14b23c68140b20978a0e4ba809f6a9fc67 100644
--- a/components/login/screens/screen_context.cc
+++ b/components/login/screens/screen_context.cc
@@ -122,6 +122,19 @@ String16List ScreenContext::GetString16List(
   return Get(key, default_value);
 }
 
+scoped_ptr<ScreenContext::KeyObserverSubscription>
+ScreenContext::AddKeyObserver(const KeyType& key, const KeyObserver& observer) {
+  auto it = key_observers_.find(key);
+  linked_ptr<KeyObserversList> observers_list;
+  if (it == key_observers_.end()) {
+    observers_list.reset(new KeyObserversList());
+    key_observers_[key] = observers_list;
+  } else {
+    observers_list = it->second;
+  }
+  return observers_list->Add(observer);
+}
+
 bool ScreenContext::HasKey(const KeyType& key) const {
   DCHECK(CalledOnValidThread());
   return storage_.HasKey(key);
@@ -147,12 +160,15 @@ void ScreenContext::ApplyChanges(const base::DictionaryValue& diff,
     keys->clear();
     keys->reserve(diff.size());
   }
-  base::DictionaryValue::Iterator it(diff);
-  while (!it.IsAtEnd()) {
+
+  for (base::DictionaryValue::Iterator it(diff); !it.IsAtEnd(); it.Advance()) {
     Set(it.key(), it.value().DeepCopy());
     if (keys)
       keys->push_back(it.key());
-    it.Advance();
+
+    linked_ptr<KeyObserversList> observers = key_observers_[it.key()];
+    if (observers.get())
+      observers->Notify(it.key(), it.value());
   }
   changes_.Clear();
 }