Add warnings and hints to for-in.

pkg/compiler/lib/src/common/names.dart

Index: pkg/compiler/lib/src/common/names.dart
diff --git a/pkg/compiler/lib/src/common/names.dart b/pkg/compiler/lib/src/common/names.dart
index 7051ffee0cd000f4948214276f88838af44f0804..5d104efd1dc6795169b0c871a140386ecce51daa 100644
--- a/pkg/compiler/lib/src/common/names.dart
+++ b/pkg/compiler/lib/src/common/names.dart
@@ -18,10 +18,17 @@ class Identifiers {
   /// The name of the call operator.
   static const String call = 'call';
 
+  /// The name of the current element property used on iterators in for-each
+  /// loops.
+  static const String current = 'current';
+
   /// The name of the from environment constructors on 'int', 'bool' and
   /// 'String'.
   static const String fromEnvironment = 'fromEnvironment';
 
+  /// The name of the iterator property used in for-each loops.
+  static const String iterator = 'iterator';
+
   /// The name of the main method.
   static const String main = 'main';
 
@@ -39,13 +46,13 @@ class Names {
 
   /// The name of the current element property used on iterators in for-each
   /// loops.
-  static const Name current = const PublicName('current');
+  static const Name current = const PublicName(Identifiers.current);
 
   /// The name of the dynamic type.
   static const Name dynamic_ = const PublicName('dynamic');
 
   /// The name of the iterator property used in for-each loops.
-  static const Name iterator = const PublicName('iterator');
+  static const Name iterator = const PublicName(Identifiers.iterator);
 
   /// The name of the move next method used on iterators in for-each loops.
   static const Name moveNext = const PublicName('moveNext');