Add an "api signature" to summaries.

pkg/analyzer/tool/summary/idl_model.dart

 // Copyright (c) 2015, 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.
 
 /**
  * This file contains a set of concrete classes representing an in-memory
  * semantic model of the IDL used to code generate summary serialization and
  * deserialization code.
  */
 library analyzer.tool.summary.idl_model;
@@ skipping 105 matching lines @@
    */
   final String typeName;
 
   /**
    * Indicates whether this field contains a list of the type specified in
    * [typeName].
    */
   final bool isList;
 
   FieldType(this.typeName, this.isList);
+
+  @override
+  String toString() => isList ? 'List<$typeName>' : typeName;
 }
 
 /**
  * Top level representation of the summary IDL.
  */
 class Idl {
   /**
    * Classes defined in the IDL.
    */
   final Map<String, ClassDeclaration> classes = <String, ClassDeclaration>{};
 
   /**
    * Enums defined in the IDL.
    */
   final Map<String, EnumDeclaration> enums = <String, EnumDeclaration>{};
 }