dart2js cps: Rewrite mutable variables to continuation parameters.

pkg/compiler/lib/src/tree_ir/tree_ir_builder.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 tree_ir_builder;
 
 import '../dart2jslib.dart' as dart2js;
 import '../elements/elements.dart';
 import '../cps_ir/cps_ir_nodes.dart' as cps_ir;
 import '../util/util.dart' show CURRENT_ELEMENT_SPANNABLE;
@@ skipping 594 matching lines @@
   Statement visitForeignCode(cps_ir.ForeignCode node) {
     if (node.codeTemplate.isExpression) {
       Expression foreignCode = new ForeignExpression(
           node.codeTemplate,
           node.type,
           node.arguments.map(getVariableUse).toList(growable: false),
           node.nativeBehavior,
           node.dependency);
       return continueWithExpression(node.continuation, foreignCode);
     } else {
-      assert(node.continuation == null);
+      assert(node.continuation.definition.body is cps_ir.Unreachable);
       return new ForeignStatement(
           node.codeTemplate,
           node.type,
           node.arguments.map(getVariableUse).toList(growable: false),
           node.nativeBehavior,
           node.dependency);
     }
   }
 
   Expression visitGetLength(cps_ir.GetLength node) {
     return new GetLength(getVariableUse(node.object));
   }
 
   Expression visitGetIndex(cps_ir.GetIndex node) {
     return new GetIndex(getVariableUse(node.object),
                         getVariableUse(node.index));
   }
 
   Expression visitSetIndex(cps_ir.SetIndex node) {
     return new SetIndex(getVariableUse(node.object),
                         getVariableUse(node.index),
                         getVariableUse(node.value));
   }
 }