Fix parent pointer issue in async rewriter.

lib/transformations/async.dart

 // Copyright (c) 2016, 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 kernel.transformations.async;
 
 import '../kernel.dart';
 import 'continuation.dart';
 
 /// A transformer that introduces temporary variables for all subexpressions
@@ skipping 303 matching lines @@
     // if (t) {
     //   t = [right] == true;
     // }
 
     // Recall that statements are emitted in reverse order, so first emit the if
     // statement, then the assignment of [left] == true, and then translate left
     // so any statements it emits occur after in the accumulated list (that is,
     // so they occur before in the corresponding block).
     var rightBody = blockOf(rightStatements);
     var result = allocateTemporary(nameIndex);
-    rightBody.statements.add(new ExpressionStatement(
+    rightBody.addStatement(new ExpressionStatement(
         new VariableSet(
             result,
             new MethodInvocation(
                 expr.right,
                 new Name('=='),
                 new Arguments(<Expression>[new BoolLiteral(true)])))));
     var then, otherwise;
     if (expr.operator == '&&') {
       then = rightBody;
       otherwise = null;
@@ skipping 49 matching lines @@
     // and emit:
     //
     // if ([condition]) {
     //   t = [left];
     // } else {
     //   t = [right];
     // }
     var result = allocateTemporary(nameIndex);
     var thenBody = blockOf(thenStatements);
     var otherwiseBody = blockOf(otherwiseStatements);
-    thenBody.statements.add(
+    thenBody.addStatement(
         new ExpressionStatement(new VariableSet(result, expr.then)));
-    otherwiseBody.statements.add(
+    otherwiseBody.addStatement(
         new ExpressionStatement(new VariableSet(result, expr.otherwise)));
     var branch = new IfStatement(expr.condition, thenBody, otherwiseBody);
     statements.add(branch);
 
     seenAwait = false;
     branch.condition = branch.condition.accept(this)..parent = branch;
 
     ++nameIndex;
     seenAwait = seenAwait || thenAwait || otherwiseAwait;
     return new VariableGet(result);
@@ skipping 73 matching lines @@
       });
     }
   }
 
   visitFunctionNode(FunctionNode node) {
     var nestedRewriter = new RecursiveContinuationRewriter(
         continuationRewriter.helper);
     return node.accept(nestedRewriter);
   }
 }