Print 'await' when for is async.

pkg/kernel/lib/text/ast_to_text.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 kernel.ast_to_text;
 
 import '../ast.dart';
 import '../import_table.dart';
 import '../type_propagation/type_propagation.dart';
 
 class Namer<T> {
@@ skipping 1130 matching lines @@
       writeExpression(node.condition);
     }
     writeComma(';');
     writeList(node.updates, writeExpression);
     writeSymbol(')');
     writeBody(node.body);
   }
 
   visitForInStatement(ForInStatement node) {
     writeIndentation();
+    if (node.isAsync) {
+      writeSpaced('await');
+    }
     writeSpaced('for');
     writeSymbol('(');
     writeVariableDeclaration(node.variable, useVarKeyword: true);
     writeSpaced('in');
     writeExpression(node.iterable);
     writeSymbol(')');
     writeBody(node.body);
   }
 
   visitSwitchStatement(SwitchStatement node) {
@@ skipping 374 matching lines @@
   }
   throw 'illegal ProcedureKind: $kind';
 }
 
 class ExpressionPrinter {
   final Printer writeer;
   final int minimumPrecedence;
 
   ExpressionPrinter(this.writeer, this.minimumPrecedence);
 }