Use summary IDL file for interface classes.

pkg/analyzer/test/src/summary/resynthesize_test.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.
 
 library test.src.serialization.elements_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/member.dart';
 import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/generated/element_handle.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/resolver.dart'
     show Namespace, TypeProvider;
 import 'package:analyzer/src/generated/source.dart';
-import 'package:analyzer/src/summary/format.dart';
+import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/summary/resynthesize.dart';
 import 'package:analyzer/src/summary/summarize_elements.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../generated/resolver_test.dart';
 import '../../reflective_tests.dart';
 
 main() {
   groupSep = ' | ';
   runReflectiveTests(ResynthTest);
@@ skipping 2460 matching lines @@
       fail('Unexpectedly tried to get unlinked summary for $uri');
     }
     return serializedUnit;
   }
 
   @override
   bool hasLibrarySummary(String uri) {
     return true;
   }
 }