Move dart2jslib parts into separate libraries.

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library elements;
 
 import '../constants/constructors.dart';
 import '../constants/expressions.dart';
+import '../dart_types.dart';
+import '../dart2jslib.dart' show
+    Backend,
+    Compiler,
+    isPrivateName,
+    SourceSpan;
+import '../diagnostic_listener.dart';
+import '../messages.dart' show MessageKind;
+import '../resolution/resolution.dart';
+import '../ordered_typeset.dart' show OrderedTypeSet;
+import '../scanner/scannerlib.dart' show
+    Token,
+    isUserDefinableOperator,
+    isMinusOperator;
+import '../script.dart';
 import '../tree/tree.dart';
 import '../util/util.dart';
-import '../resolution/resolution.dart';
-
-import '../dart2jslib.dart' show InterfaceType,
-                                 DartType,
-                                 TypeVariableType,
-                                 TypedefType,
-                                 DualKind,
-                                 MessageKind,
-                                 DiagnosticListener,
-                                 Script,
-                                 FunctionType,
-                                 Selector,
-                                 SourceSpan,
-                                 Constant,
-                                 Compiler,
-                                 Backend,
-                                 isPrivateName;
-
-import '../dart_types.dart';
-
-import '../scanner/scannerlib.dart' show Token,
-                                         isUserDefinableOperator,
-                                         isMinusOperator;
-
-import '../ordered_typeset.dart' show OrderedTypeSet;
 
 import 'visitor.dart' show ElementVisitor;
 
 part 'names.dart';
 
 const int STATE_NOT_STARTED = 0;
 const int STATE_STARTED = 1;
 const int STATE_DONE = 2;
 
 class ElementCategory {
@@ skipping 1610 matching lines @@
   bool get isDeclaredByField;
 
   /// Returns `true` if this member is abstract.
   bool get isAbstract;
 
   /// If abstract, [implementation] points to the overridden concrete member,
   /// if any. Otherwise [implementation] points to the member itself.
   Member get implementation;
 }