fix return type of computeNode.

pkg/analyzer/lib/src/dart/element/element.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 analyzer.src.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 5228 matching lines @@
       }
       buffer.write(">");
     }
     buffer.write(" = ");
     if (function != null) {
       (function as ElementImpl).appendTo(buffer);
     }
   }
 
   @override
-  FunctionTypeAlias computeNode() =>
+  GenericTypeAlias computeNode() =>
       getNodeMatching((node) => node is GenericTypeAlias);
 
   @override
   ElementImpl getChild(String identifier) {
     for (TypeParameterElement typeParameter in typeParameters) {
       TypeParameterElementImpl typeParameterImpl = typeParameter;
       if (typeParameterImpl.identifier == identifier) {
         return typeParameterImpl;
       }
     }
@@ skipping 3859 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }