Use common.dart to re-export commonly used entities.

pkg/compiler/lib/src/universe/universe.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 universe;
 
 import 'dart:collection';
 
-import '../common/resolution.dart' show
-    Resolution;
+import '../common.dart';
 import '../compiler.dart' show
     Compiler;
-import '../diagnostics/invariant.dart' show
-    invariant;
 import '../elements/elements.dart';
 import '../dart_types.dart';
 import '../util/util.dart';
 import '../world.dart' show
     ClassWorld,
     World;
 
 import 'selector.dart' show
     Selector;
 
@@ skipping 395 matching lines @@
   // TODO(ahe): Replace this method with something that is O(1), for example,
   // by using a map.
   List<LocalFunctionElement> slowDirectlyNestedClosures(Element element) {
     // Return new list to guard against concurrent modifications.
     return new List<LocalFunctionElement>.from(
         allClosures.where((LocalFunctionElement closure) {
           return closure.executableContext == element;
         }));
   }
 }