Testing support for FF and Safari

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 404 matching lines @@
 /// JavaScript class.
 registerExtension(jsType, dartExtType) => JS(
     '',
     '''(() => {
   // TODO(vsm): Not all registered js types are real.
   if (!jsType) return;
 
   let extProto = $dartExtType.prototype;
   let jsProto = $jsType.prototype;
 
+  // TODO(vsm): This sometimes doesn't exist on FF.  These types will be
+  // broken.
+  if (!jsProto) return;
+
   // Mark the JS type's instances so we can easily check for extensions.
   jsProto[$_extensionType] = $dartExtType;
   $_installProperties(jsProto, extProto);
   let originalSigFn = $getOwnPropertyDescriptor($dartExtType, $_methodSig).get;
   $assert_(originalSigFn);
   $defineMemoizedGetter($jsType, $_methodSig, originalSigFn);
 })()''');
 
 ///
 /// Mark a concrete type as implementing extension methods.
@@ skipping 96 matching lines @@
 ///
 /// The constructor
 defineNamedConstructorCallable(clazz, name, ctor) => JS(
     '',
     '''(() => {
   ctor.prototype = $clazz.prototype;
   // Use defineProperty so we don't hit a property defined on Function,
   // like `caller` and `arguments`.
   $defineProperty($clazz, $name, { value: ctor, configurable: true });
 })()''');