Fixes #479

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 104 matching lines @@
 getGenericClass(type) =>
     JS('', '$safeGetOwnProperty($type, $_originalDeclaration)');
 
 getGenericArgs(type) =>
     JS('', '$safeGetOwnProperty($type, $_typeArguments)');
 
 final _constructorSig = JS('', 'Symbol("sigCtor")');
 final _methodSig = JS('', 'Symbol("sig")');
 final _staticSig = JS('', 'Symbol("sigStatic")');
 
-/// Get the type of a method using the stored signature
+/// Get the type of a method from an object using the stored signature
 getMethodType(obj, name) => JS('', '''(() => {
   if ($obj === void 0) return void 0;
   if ($obj == null) return void 0;
-  let sigObj = $obj.__proto__.constructor[$_methodSig];
+  return $getMethodTypeFromType($obj.__proto__.constructor, $name);
+})()''');
+
+/// Get the type of a method from a type using the stored signature
+getMethodTypeFromType(type, name) => JS('', '''(() => {
+  let sigObj = $type[$_methodSig];
   if (sigObj === void 0) return void 0;
   let parts = sigObj[$name];
   if (parts === void 0) return void 0;
   return $definiteFunctionType.apply(null, parts);
 })()''');
 
 /// Get the type of a constructor from a class using the stored signature
 /// If name is undefined, returns the type of the default constructor
 /// Returns undefined if the constructor is not found.
 classGetConstructorType(cls, name) => JS('', '''(() => {
@@ skipping 227 matching lines @@
 })()''');
 
 /// Sets the element type of a list literal.
 list(obj, elementType) =>
     JS('', '$setType($obj, ${getGenericClass(JSArray)}($elementType))');
 
 setBaseClass(derived, base) => JS('', '''(() => {
   // Link the extension to the type it's extending as a base class.
   $derived.prototype.__proto__ = $base.prototype;
 })()''');