Model 'await for' as an explicit node in tree and fix its handling.

pkg/compiler/lib/src/tree/prettyprint.dart

 // Copyright (c) 2012, 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.
 
 part of tree;
 
 /**
  * Pretty-prints Node tree in XML-like format.
  *
  * TODO(smok): Add main() to run from command-line to print out tree for given
@@ skipping 172 matching lines @@
   }
 
   visitExpressionStatement(ExpressionStatement node) {
     visitNodeWithChildren(node, "ExpressionStatement");
   }
 
   visitFor(For node) {
     visitNodeWithChildren(node, "For");
   }
 
-  visitForIn(ForIn node) {
-    openNode(node, "ForIn", {'await': node.awaitToken});
+  visitAsyncForIn(AsyncForIn node) {
+    openNode(node, "AsyncForIn");
+  }
+
+  visitSyncForIn(SyncForIn node) {
+    openNode(node, "ForIn");
     node.visitChildren(this);
     closeNode();
   }
 
   visitFunctionDeclaration(FunctionDeclaration node) {
     visitNodeWithChildren(node, "FunctionDeclaration");
   }
 
   visitFunctionExpression(FunctionExpression node) {
     openNode(node, "FunctionExpression", {
@@ skipping 323 matching lines @@
   }
 
   visitGotoStatement(GotoStatement node) {
     unimplemented('visitNode', node: node);
   }
 
   unimplemented(String message, {Node node}) {
     throw message;
   }
 }