Make elements/names.dart its own library

pkg/compiler/lib/src/elements/elements.dart

Index: pkg/compiler/lib/src/elements/elements.dart
diff --git a/pkg/compiler/lib/src/elements/elements.dart b/pkg/compiler/lib/src/elements/elements.dart
index 6cf201cd7f6f90f688991d5d167f240318291a78..906db4ffba55e2696647909026b288581816550e 100644
--- a/pkg/compiler/lib/src/elements/elements.dart
+++ b/pkg/compiler/lib/src/elements/elements.dart
@@ -20,16 +20,14 @@ import 'package:front_end/src/fasta/scanner.dart'
     show Token, isUserDefinableOperator, isMinusOperator;
 import '../tree/tree.dart' hide AsyncModifier;
 import '../universe/call_structure.dart';
-import 'package:front_end/src/fasta/scanner/characters.dart' show $_;
 import '../util/util.dart';
 import '../world.dart' show ClosedWorld;
 import 'entities.dart';
+import 'names.dart';
 import 'resolution_types.dart';
 import 'types.dart';
 import 'visitor.dart' show ElementVisitor;
 
-part 'names.dart';
-
 const int STATE_NOT_STARTED = 0;
 const int STATE_STARTED = 1;
 const int STATE_DONE = 2;