Add an UNDEFINED_IDENTIFIER_AWAIT warning

pkg/analyzer/lib/src/generated/error.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.
 
 library analyzer.src.generated.error;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart' show AstNode;
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 5742 matching lines @@
    * initializer and there is no declaration <i>d</i> with name <i>id</i> in the
    * lexical scope enclosing the expression.
    *
    * Parameters:
    * 0: the name of the identifier
    */
   static const StaticWarningCode UNDEFINED_IDENTIFIER =
       const StaticWarningCode('UNDEFINED_IDENTIFIER', "Undefined name '{0}'");
 
   /**
+   * If the identifer is 'await', be helpful about it.
+   */
+  static const StaticWarningCode UNDEFINED_IDENTIFIER_AWAIT =
+      const StaticWarningCode('UNDEFINED_IDENTIFIER_AWAIT',
+          "Undefined name 'await'; did you mean to add the 'async' marker to '{0}'?");
+
+  /**
    * 12.14.2 Binding Actuals to Formals: Furthermore, each <i>q<sub>i</sub></i>,
    * <i>1<=i<=l</i>, must have a corresponding named parameter in the set
    * {<i>p<sub>n+1</sub></i> &hellip; <i>p<sub>n+k</sub></i>} or a static
    * warning occurs.
    *
    * Parameters:
    * 0: the name of the requested named parameter
    */
   static const StaticWarningCode UNDEFINED_NAMED_PARAMETER =
       const StaticWarningCode('UNDEFINED_NAMED_PARAMETER',
@@ skipping 317 matching lines @@
    * Initialize a newly created error code to have the given [name].
    */
   const TodoCode(String name) : super(name, "{0}");
 
   @override
   ErrorSeverity get errorSeverity => ErrorSeverity.INFO;
 
   @override
   ErrorType get type => ErrorType.TODO;
 }