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..93a1c92476e47199e70f4163175acd7c2a4f225f 100644
--- a/components/login/screens/screen_context.cc
+++ b/components/login/screens/screen_context.cc
@@ -147,12 +147,11 @@ 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();
   }
   changes_.Clear();
 }