MutableVariable no longer has a host Element.

pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart

Index: pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
diff --git a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
index 8d5c2fbe49f6e1f1d18074e5001c921254f5b5e7..a8ede5cef1cd67e216989af369e0f2a46407110b 100644
--- a/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
+++ b/pkg/compiler/lib/src/tree_ir/tree_ir_builder.dart
@@ -82,7 +82,6 @@ class Builder implements cps_ir.Visitor<Node> {
   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;
@@ -90,7 +89,7 @@ class Builder implements cps_ir.Visitor<Node> {
   }
 
   Variable getMutableVariable(cps_ir.MutableVariable mutableVariable) {
-    if (mutableVariable.host != currentElement) {
+    if (!mutable2variable.containsKey(mutableVariable)) {
       return parent.getMutableVariable(mutableVariable)..isCaptured = true;
     }
     return mutable2variable[mutableVariable];