NPE fix in ExitDetector visitor- in analyzer pkg

pkg/analyzer/lib/src/generated/resolver.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 engine.resolver;
 
 import "dart:math" as math;
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/utilities_collection.dart';
@@ skipping 3889 matching lines @@
   bool visitAsExpression(AsExpression node) => _nodeExits(node.expression);
 
   @override
   bool visitAssertStatement(AssertStatement node) => _nodeExits(node.condition);
 
   @override
   bool visitAssignmentExpression(AssignmentExpression node) =>
       _nodeExits(node.leftHandSide) || _nodeExits(node.rightHandSide);
 
   @override
+  bool visitAwaitExpression(AwaitExpression node) =>
+      _nodeExits(node.expression);
+
+  @override
   bool visitBinaryExpression(BinaryExpression node) {
     Expression lhsExpression = node.leftOperand;
     sc.TokenType operatorType = node.operator.type;
     // If the operator is || and the left hand side is false literal, don't
     // consider the RHS of the binary expression.
     // TODO(jwren) Do we want to take constant expressions into account,
     // evaluate if(false) {} differently than if(<condition>), when <condition>
     // evaluates to a constant false value?
     if (operatorType == sc.TokenType.BAR_BAR) {
       if (lhsExpression is BooleanLiteral) {
@@ skipping 11751 matching lines @@
    * library.
    */
   final HashSet<String> members = new HashSet<String>();
 
   /**
    * Names of resolved or unresolved class members that are read in the
    * library.
    */
   final HashSet<String> readMembers = new HashSet<String>();
 }