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

pkg/compiler/lib/src/closure.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.
 
 library closureToClassMapper;
 
 import "elements/elements.dart";
 import "dart2jslib.dart";
 import "dart_types.dart";
 import "js_backend/js_backend.dart" show JavaScriptBackend;
@@ skipping 1051 matching lines @@
   }
 
   visitTryStatement(TryStatement node) {
     // TODO(ngeoffray): implement finer grain state.
     bool oldInTryStatement = inTryStatement;
     inTryStatement = true;
     node.visitChildren(this);
     inTryStatement = oldInTryStatement;
   }
 
-  visitForIn(ForIn node) {
-    if (node.awaitToken != null) {
-      // An `await for` loop is enclosed in an implicit try-finally.
-      bool oldInTryStatement = inTryStatement;
-      inTryStatement = true;
-      visitLoop(node);
-      inTryStatement = oldInTryStatement;
-    } else {
-      visitLoop(node);
-    }
+  visitAsyncForIn(AsyncForIn node) {
+    // An `await for` loop is enclosed in an implicit try-finally.
+    bool oldInTryStatement = inTryStatement;
+    inTryStatement = true;
+    visitLoop(node);
+    inTryStatement = oldInTryStatement;
   }
 }
 
 /// A type variable as a local variable.
 class TypeVariableLocal implements Local {
   final TypeVariableType typeVariable;
   final ExecutableElement executableContext;
 
   TypeVariableLocal(this.typeVariable, this.executableContext);
 
   String get name => typeVariable.name;
 
   int get hashCode => typeVariable.hashCode;
 
   bool operator ==(other) {
     if (other is! TypeVariableLocal) return false;
     return typeVariable == other.typeVariable;
   }
 }