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

pkg/compiler/lib/src/inferrer/inferrer_visitor.dart

 // Copyright (c) 2013, 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 inferrer_visitor;
 
 import '../dart2jslib.dart' hide Selector, TypedSelector;
 import '../dart_types.dart';
 import '../elements/elements.dart';
 import '../tree/tree.dart';
@@ skipping 251 matching lines @@
  */
 class ArgumentsTypes<T> extends IterableMixin<T> {
   final List<T> positional;
   final Map<String, T> named;
   ArgumentsTypes(this.positional, named)
     : this.named = (named == null || named.isEmpty) ? const {} : named {
     assert(this.positional.every((T type) => type != null));
     assert(this.named.values.every((T type) => type != null));
   }
 
+  ArgumentsTypes.empty() : positional = const [], named = const {};
+
   int get length => positional.length + named.length;
 
   Iterator<T> get iterator => new ArgumentsTypesIterator(this);
 
   String toString() => "{ positional = $positional, named = $named }";
 
   bool operator==(other) {
     if (positional.length != other.positional.length) return false;
     if (named.length != other.named.length) return false;
     for (int i = 0; i < positional.length; i++) {
@@ skipping 424 matching lines @@
   T visitSuperSend(Send node);
 
   T visitStaticSend(Send node);
 
   T visitGetterSend(Send node);
 
   T visitClosureSend(Send node);
 
   T visitDynamicSend(Send node);
 
-  T visitForIn(ForIn node);
+  T visitAsyncForIn(AsyncForIn node);
+
+  T visitSyncForIn(SyncForIn node);
 
   T visitReturn(Return node);
 
   T visitFunctionExpression(FunctionExpression node);
 
   T visitAssertSend(Send node) {
     if (!compiler.enableUserAssertions) {
       return types.nullType;
     }
     // TODO(johnniwinther): Don't handle assert like a regular static call since
@@ skipping 574 matching lines @@
     return type;
   }
 
   T visitCascade(Cascade node) {
     // Ignore the result of the cascade send and return the type of the cascade
     // receiver.
     visit(node.expression);
     return cascadeReceiverStack.removeLast();
   }
 }