Use summary IDL file for interface classes.

pkg/analyzer/test/src/summary/summarize_ast_test.dart

 // Copyright (c) 2016, 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.test.src.summary.summarize_ast_test;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/parser.dart';
 import 'package:analyzer/src/generated/scanner.dart';
-import 'package:analyzer/src/summary/format.dart';
+import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/summary/prelink.dart';
 import 'package:analyzer/src/summary/summarize_ast.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../reflective_tests.dart';
 import 'summary_common.dart';
 
 main() {
   groupSep = ' | ';
   runReflectiveTests(UnlinkedSummarizeAstTest);
@@ skipping 85 matching lines @@
   CompilationUnit _parseText(String text) {
     CharSequenceReader reader = new CharSequenceReader(text);
     Scanner scanner =
         new Scanner(null, reader, AnalysisErrorListener.NULL_LISTENER);
     Token token = scanner.tokenize();
     Parser parser = new Parser(null, AnalysisErrorListener.NULL_LISTENER);
     parser.parseGenericMethods = true;
     return parser.parseCompilationUnit(token);
   }
 }