Replace 'length' with more generic 'extractProperty' operation.

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/dart/ast/token.dart';
 import 'package:analyzer/src/dart/scanner/reader.dart';
@@ skipping 155 matching lines @@
   @override
   bool get checkAstDerivedData => true;
 
   @override
   bool get expectAbsoluteUrisInDependencies => false;
 
   @override
   bool get skipFullyLinkedData => false;
 
   @override
+  bool get skipNonConstInitializers => false;
+
+  @override
   addNamedSource(String filePath, String contents) {
     CompilationUnit unit = _parseText(contents);
     UnlinkedUnit unlinkedUnit =
         new UnlinkedUnit.fromBuffer(serializeAstUnlinked(unit).toBuffer());
     uriToUnit[absUri(filePath)] = unlinkedUnit;
   }
 
   @override
   void serializeLibraryText(String text, {bool allowErrors: false}) {
     Uri testDartUri = Uri.parse(absUri('/test.dart'));
@@ skipping 47 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);
   }
 }