MutableVariable no longer has a host Element.

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 '../dart_types.dart';
 import '../elements/elements.dart';
 import '../cps_ir/cps_ir_nodes.dart' as cps_ir;
@@ skipping 64 matching lines @@
 
   Builder createInnerBuilder() {
     return new Builder(internalError, this);
   }
 
   /// Variable used in [buildPhiAssignments] as a temporary when swapping
   /// variables.
   Variable phiTempVar;
 
   Variable addMutableVariable(cps_ir.MutableVariable irVariable) {
-    assert(irVariable.host == currentElement);
     assert(!mutable2variable.containsKey(irVariable));
     Variable variable = new Variable(currentElement, irVariable.hint);
     mutable2variable[irVariable] = variable;
     return variable;
   }
 
   Variable getMutableVariable(cps_ir.MutableVariable mutableVariable) {
-    if (mutableVariable.host != currentElement) {
+    if (!mutable2variable.containsKey(mutableVariable)) {
       return parent.getMutableVariable(mutableVariable)..isCaptured = true;
     }
     return mutable2variable[mutableVariable];
   }
 
   VariableUse getMutableVariableUse(
         cps_ir.Reference<cps_ir.MutableVariable> reference) {
     Variable variable = getMutableVariable(reference.definition);
     return new VariableUse(variable);
   }
@@ skipping 572 matching lines @@
 
   Statement visitSetStatic(cps_ir.SetStatic node) {
     SetStatic setStatic = new SetStatic(
         node.element,
         getVariableUse(node.value),
         node.sourceInformation);
     return new ExpressionStatement(setStatic, visit(node.body));
   }
 }