Mark the local for this as used if a constructor call needs type variables.

lib/compiler/implementation/closure.dart

 // Copyright (c) 2012, 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("closureToClassMapper");
 
 #import("elements/elements.dart");
 #import("leg.dart");
 #import("scanner/scannerlib.dart");
 #import("tree/tree.dart");
@@ skipping 299 matching lines @@
   }
 
   visitSendSet(SendSet node) {
     Element element = elements[node];
     if (Elements.isLocal(element)) {
       mutatedVariables.add(element);
     }
     super.visitSendSet(node);
   }
 
+  visitNewExpression(NewExpression node) {
+    bool hasTypeVariable(DartType type) {
+      if (type is TypeVariableType) {
+        return true;
+      } else if (type is InterfaceType) {
+        InterfaceType ifcType = type;
+        for (DartType argument in ifcType.arguments) {
+          if (hasTypeVariable(argument)) {
+            return true;
+          }
+        }
+      }
+      return false;
+    }
+    TypeAnnotation annotation = node.send.getTypeAnnotation();
+    DartType type = elements.getType(annotation);
+    if (hasTypeVariable(type)) {
+      if (closureData.thisElement !== null) {

[floitsch, 2012/09/03 14:04:15]

Add comment why this is necessary. Maybe find a more direct way of testing it?
for example: closureData.isInsideInstanceMethod

+        useLocal(closureData.thisElement);
+      }
+    }
+    node.visitChildren(this);
+  }
+
   // If variables that are declared in the [node] scope are captured and need
   // to be boxed create a box-element and update the [capturingScopes] in the
   // current [closureData].
   // The boxed variables are updated in the [capturedVariableMapping].
   void attachCapturedScopeVariables(Node node) {
     Element box = null;
     Map<Element, Element> scopeMapping = new Map<Element, Element>();
     for (Element element in scopeVariables) {
       // No need to box non-assignable elements.
       if (!element.isAssignable()) continue;
@@ skipping 169 matching lines @@
   }
 
   visitTryStatement(TryStatement node) {
     // TODO(ngeoffray): implement finer grain state.
     bool oldInTryStatement = inTryStatement;
     inTryStatement = true;
     node.visitChildren(this);
     inTryStatement = oldInTryStatement;
   }
 }