Change Enqueuer to use Entity instead of Element.

tests/compiler/dart2js/mirrors_used_test.dart

 // Copyright (c) 2013, 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.
 
 /// Test that the @MirrorsUsed annotation suppress hints and that only
 /// requested elements are retained for reflection.
 library dart2js.test.mirrors_used_test;
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
@@ skipping 109 matching lines @@
           Expect.isFalse(
               compiler.backend.isAccessibleByReflection(member), '$member');
         }
       });
     }
 
     int metadataCount = 0;
     Set<ConstantValue> compiledConstants = backend.constants.compiledConstants;
     // Make sure that most of the metadata constants aren't included in the
     // generated code.
-    backend.processMetadata(compiler.enqueuer.resolution.processedElements,
+    backend.processMetadata(compiler.enqueuer.resolution.processedEntities,
         (metadata) {
       ConstantValue constant =
           backend.constants.getConstantValueForMetadata(metadata);
       Expect.isFalse(
           compiledConstants.contains(constant), constant.toStructuredText());
       metadataCount++;
     });
 
     // There should at least be one metadata constant:
     // 1. The constructed constant for 'MirrorsUsed'.
@@ skipping 39 matching lines @@
 library lib;
 
 import 'dart:mirrors';
 
 useReflect(type) {
   print(new Symbol('Foo'));
   print(MirrorSystem.getName(reflectClass(type).owner.qualifiedName));
 }
 """,
 };