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

lib/compiler/implementation/tree/nodes.dart

Index: lib/compiler/implementation/tree/nodes.dart
diff --git a/lib/compiler/implementation/tree/nodes.dart b/lib/compiler/implementation/tree/nodes.dart
index 7fd2edc2f94d53524b1c36c5a86166b7582235ad..307b72a9f8b66b32b5e4597cf829b666dce0cddd 100644
--- a/lib/compiler/implementation/tree/nodes.dart
+++ b/lib/compiler/implementation/tree/nodes.dart
@@ -305,6 +305,22 @@ class Send extends Expression {
     assert(receiver === null);
     return new Send(newReceiver, selector, argumentsNode);
   }
+
+  /**
+   * Returns the type annotation of a connstructor call in an object
+   * instantiation.
+   */
+  TypeAnnotation getTypeAnnotation() {
+    if (selector is TypeAnnotation) {
+      return selector;
+    } else if (selector is Send) {
+      Send selectorSend = selector;
+      if (selectorSend.receiver is TypeAnnotation) {
+        return selectorSend.receiver;
+      }
+    }
+    return null;
+  }
 }
 
 class Postfix extends NodeList {