Respect the "allowErrors" parameter in _ResynthesizeAstTest.checkLibrary.

pkg/analyzer/test/src/summary/resynthesize_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.resynthesize_ast_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/generated/engine.dart'
     show AnalysisContext, AnalysisOptionsImpl;
 import 'package:analyzer/src/generated/sdk.dart';
 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/link.dart';
 import 'package:analyzer/src/summary/prelink.dart';
 import 'package:analyzer/src/summary/resynthesize.dart';
@@ skipping 855 matching lines @@
 }
 
 abstract class _ResynthesizeAstTest extends ResynthesizeTest
     with _AstResynthesizeTestMixin {
   @override
   LibraryElementImpl checkLibrary(String text,
       {bool allowErrors: false, bool dumpSummaries: false}) {
     Source source = addTestSource(text);
     LibraryElementImpl resynthesized = _encodeDecodeLibraryElement(source);
     LibraryElementImpl original = context.computeLibraryElement(source);
+    if (!allowErrors) {
+      List<AnalysisError> errors = context.computeErrors(source);
+      if (errors.isNotEmpty) {
+        fail('Analysis errors: $errors');
+      }
+    }
     checkLibraryElements(original, resynthesized);
     return resynthesized;
   }
 
   @override
   void compareLocalElementsOfExecutable(ExecutableElement resynthesized,
       ExecutableElement original, String desc) {
     // We don't resynthesize local elements during link.
     // So, we should not compare them.
   }
 
   @override
   DartSdk createDartSdk() => AbstractContextTest.SHARED_MOCK_SDK;
 
   @override
   TestSummaryResynthesizer encodeDecodeLibrarySource(Source source) {
     return _encodeLibrary(source);
   }
 }