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

pkg/compiler/lib/src/cps_ir/insert_refinements.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 cps_ir.optimization.insert_refinements;
 
-import 'optimizers.dart' show Pass;
-import 'shrinking_reductions.dart' show ParentVisitor;
+import '../common/names.dart';
+import '../types/types.dart' show
+    TypeMask;
+
 import 'cps_ir_nodes.dart';
-import '../types/constants.dart';
-import '../constants/values.dart';
-import '../common/names.dart';
-import '../universe/universe.dart';
-import '../elements/elements.dart';
-import '../types/types.dart' show TypeMask;
+import 'optimizers.dart' show
+    Pass;
+import 'shrinking_reductions.dart' show
+    ParentVisitor;
 import 'type_mask_system.dart';
 
 /// Inserts [Refinement] nodes in the IR to allow for sparse path-sensitive
 /// type analysis in the [TypePropagator] pass.
 ///
 /// Refinement nodes are inserted at the arms of a [Branch] node with a
 /// condition of form `x is T` or `x == null`.
 ///
 /// Refinement nodes are inserted after a method invocation to refine the
 /// receiver to the types that can respond to the given selector.
@@ skipping 189 matching lines @@
            cont.firstRef.parent is Branch)) {
         // Do not push the continuation here.
         // visitInvokeMethod and visitBranch will do that.
       } else {
         push(cont);
       }
     }
     return node.body;
   }
 }