Make the universe parts into small libraries.

pkg/compiler/lib/src/resolution/tree_elements.dart

 // Copyright (c) 2015, 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 dart2js.resolution.tree_elements;
 
 import '../constants/expressions.dart';
 import '../dart_types.dart';
 import '../diagnostics/invariant.dart' show
     invariant;
 import '../diagnostics/spannable.dart' show
     Spannable;
 import '../elements/elements.dart';
 import '../types/types.dart' show
     TypeMask;
 import '../tree/tree.dart';
 import '../util/util.dart';
+import '../universe/call_structure.dart' show
+    CallStructure;
+import '../universe/selector.dart' show
+    Selector;
 import '../universe/universe.dart' show
-    CallStructure,
-    Selector,
-    SelectorKind,
     UniverseSelector;
 
 import 'secret_tree_element.dart' show getTreeElement, setTreeElement;
 import 'send_structure.dart';
 
 abstract class TreeElements {
   AnalyzableElement get analyzedElement;
   Iterable<Node> get superUses;
 
   /// Iterables of the dependencies that this [TreeElement] records of
@@ skipping 518 matching lines @@
   }
 
   void setCurrentTypeMask(ForIn node, TypeMask mask) {
     _setTypeMask(node.inToken, mask);
   }
 
   TypeMask getCurrentTypeMask(ForIn node) {
     return _getTypeMask(node.inToken);
   }
 }