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

pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart

 // Copyright (c) 2014, 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 dart_tree_printer;
 
 import '../constants/values.dart' as values;
 import '../dart_types.dart' as types;
 import '../dart2jslib.dart' as dart2js;
 import '../elements/elements.dart' as elements;
@@ skipping 757 matching lines @@
           makeList(',', stmt.updates.map(makeExpression)),
           makeStatement(stmt.body, shortIf: shortIf),
           forToken);
     } else if (stmt is ForIn) {
       tree.Node left;
       if (stmt.leftHandValue is Identifier) {
         left = makeExpression(stmt.leftHandValue);
       } else {
         left = makeVariableDeclarations(stmt.leftHandValue);
       }
-      return new tree.ForIn(
+      return new tree.SyncForIn(
           left,
           makeExpression(stmt.expression),
           makeStatement(stmt.body, shortIf: shortIf),
-          awaitToken,
           forToken,
           inToken);
     } else if (stmt is FunctionDeclaration) {
       tree.FunctionExpression function = new tree.FunctionExpression(
           stmt.name != null ? makeIdentifier(stmt.name) : null,
           makeParameters(stmt.parameters),
           makeFunctionBody(stmt.body),
           stmt.returnType != null ? makeType(stmt.returnType) : null,
           makeEmptyModifiers(),
           null,  // initializers
@@ skipping 540 matching lines @@
             printStringChunk(chunk.previous),
             node);
       } else {
         return node;
       }
     }
     return printStringChunk(output.chunk);
   }
 
 }