Add MemberEntity.isAbstract and use MemberEntity in function_set.dart

pkg/compiler/lib/src/inferrer/node_tracer.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.
 
 library compiler.src.inferrer.node_tracer;
 
 import '../common/names.dart' show Identifiers;
 import '../compiler.dart' show Compiler;
 import '../elements/elements.dart';
 import '../types/types.dart' show ContainerTypeMask, MapTypeMask;
@@ skipping 363 matching lines @@
         bailoutIfReaches(isParameterOfListAddingMethod);
       }
     }
 
     if (info.targetsIncludeComplexNoSuchMethod(inferrer) &&
         info.arguments != null &&
         info.arguments.contains(currentUser)) {
       bailout('Passed to noSuchMethod');
     }
 
-    Iterable<Element> inferredTargetTypes = info.targets.map((element) {
+    Iterable<Element> inferredTargetTypes =
+        info.targets.map((MemberElement element) {
       return inferrer.types.getInferredTypeOf(element);
     });
     if (inferredTargetTypes.any((user) => user == currentUser)) {
       addNewEscapeInformation(info);
     }
   }
 
   /**
    * Check whether element is the parameter of a list adding method.
    * The definition of what a list adding method is has to stay in sync with
@@ skipping 64 matching lines @@
     }
     if (isParameterOfListAddingMethod(element) ||
         isParameterOfMapAddingMethod(element)) {
       // These elements are being handled in
       // [visitDynamicCallSiteTypeInformation].
       return;
     }
     addNewEscapeInformation(info);
   }
 }