Fix type inference for self-recursive functions

lib/compiler/implementation/dart_backend/backend.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.
 
 class DartBackend extends Backend {
   final List<CompilerTask> tasks;
   final UnparseValidator unparseValidator;
 
   Map<Element, TreeElements> get resolvedElements() =>
       compiler.enqueuer.resolution.resolvedElements;
   Map<ClassElement, Set<Element>> resolvedClassMembers;
 
   DartBackend(Compiler compiler, [bool validateUnparse = false])
       : tasks = <CompilerTask>[],
       unparseValidator = new UnparseValidator(compiler, validateUnparse),
       resolvedClassMembers = new Map<ClassElement, Set<Element>>(),
       super(compiler) {
     tasks.add(unparseValidator);
   }
 
   void enqueueHelpers(Enqueuer world) {
     // TODO(antonm): Implement this method, if needed.
   }
 
-  CodeBuffer codegen(WorkItem work) { return new CodeBuffer(); }
+  void codegen(WorkItem work) { }
 
   void processNativeClasses(Enqueuer world,
                             Collection<LibraryElement> libraries) {
   }
 
   /**
    * Adds given class element with its member element to resolved classes
    * collections.
    */
   void addMemberToClass(Element element, ClassElement classElement) {
@@ skipping 126 matching lines @@
     }
     typeAnnotation.visitChildren(this);
   }
 
   void collect() {
     compiler.withCurrentElement(rootElement, () {
       rootElement.parseNode(compiler).accept(this);
     });
   }
 }