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

pkg/compiler/lib/src/typechecker.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 dart2js;
 
 class TypeCheckerTask extends CompilerTask {
   TypeCheckerTask(Compiler compiler) : super(compiler);
   String get name => "Type checker";
 
@@ skipping 1701 matching lines @@
   }
 
   visitBreakStatement(BreakStatement node) {
     return const StatementType();
   }
 
   visitContinueStatement(ContinueStatement node) {
     return const StatementType();
   }
 
-  visitForIn(ForIn node) {
+  visitAsyncForIn(AsyncForIn node) {
     analyze(node.expression);
     analyze(node.body);
     return const StatementType();
+  }
+
+  visitSyncForIn(SyncForIn node) {
+    analyze(node.expression);
+    analyze(node.body);
+    return const StatementType();
   }
 
   visitLabeledStatement(LabeledStatement node) {
     return analyze(node.statement);
   }
 
   visitLiteralMap(LiteralMap node) {
     InterfaceType mapType = elements.getType(node);
     DartType mapKeyType = firstType(mapType.typeArguments);
     DartType mapValueType = secondType(mapType.typeArguments);
@@ skipping 105 matching lines @@
 
   visitTypedef(Typedef node) {
     // Do not typecheck [Typedef] nodes.
   }
 
   visitNode(Node node) {
     compiler.internalError(node,
         'Unexpected node ${node.getObjectDescription()} in the type checker.');
   }
 }