Attach type info to extension method and object 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 318 matching lines @@
 
     // Mark the JS type's instances so we can easily check for extensions.
     assert(jsProto[_extensionType] === void 0);
     jsProto[_extensionType] = extProto;
 
     let dartObjProto = core.Object.prototype;
     while (extProto !== dartObjProto && extProto !== jsProto) {
       copyTheseProperties(jsProto, extProto, getOwnPropertySymbols(extProto));
       extProto = extProto.__proto__;
     }
+    let originalSigFn = getOwnPropertyDescriptor(dartExtType, _methodSig).get;
+    assert(originalSigFn);
+    defineMemoizedGetter(jsType, _methodSig, originalSigFn);
   }
   exports.registerExtension = registerExtension;
 
   /**
    * Mark a concrete type as implementing extension methods.
    * For example: `class MyIter implements Iterable`.
    *
    * This takes a list of names, which are the extension methods implemented.
    * It will add a forwarder, so the extension method name redirects to the
    * normal Dart method name. For example:
@@ skipping 50 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;
 
 });