Tighten up handling of JS types and add test.

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/classes.dart

 // 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 253 matching lines @@
 /// and also binds the object.
 ///
 /// If the optional `f` argument is passed in, it will be used as the method.
 /// This supports cases like `super.foo` where we need to tear off the method
 /// from the superclass, not from the `obj` directly.
 /// TODO(leafp): Consider caching the tearoff on the object?
 bind(obj, name, f) => JS(
     '',
     '''(() => {
   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 = $getMethodType($getType($obj), $name);
-  $assert_(sig);
+
+  // JS interop case: do not bind this for compatibility with the dart2js
+  // implementation where we cannot bind this reliably here until we trust
+  // types more.
+  if (sig === void 0) return $f;
+
+  $f = $f.bind($obj);
   $tag($f, sig);
   return $f;
 })()''');
 
 /// Instantiate a generic method.
 ///
 /// We need to apply the type arguments both to the function, as well as its
 /// associated function type.
 gbind(f, @rest typeArgs) {
   var result = JS('', '#.apply(null, #)', f, typeArgs);
@@ skipping 349 matching lines @@
     '''(() => {
   let values = [];
   for (var i = 0; i < $names.length; i++) {
     let value = $const_(new $enumClass(i));
     values.push(value);
     Object.defineProperty($enumClass, $names[i],
         { value: value, configurable: true });
   }
   $enumClass.values = $constList(values, $enumClass);
 })()''');