add support for native methods in class

pkg/analyzer/test/generated/parser_test.dart

 // Copyright (c) 2014, 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.
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_ast_factory.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/error/listener.dart';
@@ skipping 922 matching lines @@
     ClassMember member = parser.parseClassMember('C');
     assertNoErrors();
     expect(member, new isInstanceOf<MethodDeclaration>());
     expect((member as MethodDeclaration).body,
         new isInstanceOf<ExpressionFunctionBody>());
   }
 
   void test_parseClassMember_method_native() {
     createParser('m() native "str";');
     var method = parser.parseClassMember('C') as MethodDeclaration;
-    assertNoErrors();
+    if (!allowNativeClause) {
+      assertErrorsWithCodes([
+        ParserErrorCode.NATIVE_CLAUSE_SHOULD_BE_ANNOTATION,
+      ]);
+    } else {
+      assertNoErrors();
+    }
 
     var body = method.body as NativeFunctionBody;
     expect(body.nativeKeyword, isNotNull);
     expect(body.stringLiteral, isNotNull);
+    expect(body.stringLiteral?.stringValue, "str");
     expect(body.semicolon, isNotNull);
   }
 
   void test_parseClassMember_method_operator_noType() {
     createParser('operator() {}');
     ClassMember member = parser.parseClassMember('C');
     expect(member, isNotNull);
     assertNoErrors();
     expect(member, new isInstanceOf<MethodDeclaration>());
     MethodDeclaration method = member;
@@ skipping 14509 matching lines @@
     expectCommentText(typeVariable.documentationComment, '/// Doc');
   }
 
   /**
    * Assert that the given [name] is in declaration context.
    */
   void _assertIsDeclarationName(SimpleIdentifier name) {
     expect(name.inDeclarationContext(), isTrue);
   }
 }