fixes #314, super method tear offs

lib/runtime/_classes.js

 // Copyright (c) 2015, 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.
 
 /* This library defines the operations that define and manipulate Dart
  * classes.  Included in this are:
  *   - Generics
  *   - Class metadata
  *   - Extension methods
  */
@@ skipping 175 matching lines @@
     let parts = sigCtor[name];
     if (parts === void 0) return void 0;
     return types.definiteFunctionType.apply(null, parts);
   }
   exports.classGetConstructorType = _getConstructorType;
 
   /// Given an object and a method name, tear off the method.
   /// Sets the runtime type of the torn off method appropriately,
   /// and also binds the object.
   /// TODO(leafp): Consider caching the tearoff on the object?
-  function bind(obj, name) {
-    let f = obj[name].bind(obj);
+  function bind(obj, name, f) {

[Leaf, 2015/09/10 17:42:41]

Update the comment to describe the role of f?

[Jennifer Messerly, 2015/09/10 19:23:08]

Nice catch! Done!

+    if (f === void 0) f = obj[name];
+    f = f.bind(obj);
+    // TODO(jmesserly): track the function's signature on the function, instead
+    // of having to go back to the class?
     let sig = _getMethodType(obj, name);
     assert(sig);
     rtti.tag(f, sig);
     return f;
   }
   exports.bind = bind;
 
   // Set up the method signature field on the constructor
   function _setMethodSignature(f, sigF) {
     defineMemoizedGetter(f, _methodSig, () => {
@@ skipping 194 matching lines @@
   }
   exports.list = list;
 
   function setBaseClass(derived, base) {
     // Link the extension to the type it's extending as a base class.
     derived.prototype.__proto__ = base.prototype;
   }
   exports.setBaseClass = setBaseClass;
 
 });