Use Entity instead of Element in ConstantValue

pkg/compiler/lib/src/deferred_load.dart

 // Copyright (c) 2014, 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 deferred_load;
 
 import 'common/backend_api.dart' show Backend;
 import 'common/tasks.dart' show CompilerTask;
 import 'common.dart';
 import 'compiler.dart' show Compiler;
@@ skipping 526 matching lines @@
               element: dependency,
               import: new _DeclaredDeferredImport(deferredImport));
         }
       } else {
         _mapDependencies(element: dependency, import: import);
       }
     }
 
     for (ConstantValue dependency in dependentConstants) {
       if (dependency is DeferredConstantValue) {
-        _mapConstantDependencies(dependency,
-            new _DeclaredDeferredImport(dependency.prefix.deferredImport));
+        PrefixElement prefix = dependency.prefix;
+        _mapConstantDependencies(
+            dependency, new _DeclaredDeferredImport(prefix.deferredImport));
       } else {
         _mapConstantDependencies(dependency, import);
       }
     }
   }
 
   /// Adds extra dependencies coming from mirror usage.
   ///
   /// The elements are added with [_mapDependencies].
   void _addMirrorElements() {
@@ skipping 489 matching lines @@
 
   bool operator ==(other) {
     if (other is! _DeclaredDeferredImport) return false;
     return declaration == other.declaration;
   }
 
   int get hashCode => declaration.hashCode * 17;
 
   String toString() => '$declaration';
 }