Support for a dart2js `dartDeferredLoader` hook.

sdk/lib/_internal/compiler/js_lib/preambles/jsshell.js

-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
 // Javascript preamble, that lets the output of dart2js run on JSShell.
 
 (function(self) {
   // Using strict mode to avoid accidentally defining global variables.
   "use strict"; // Should be first statement of this function.
 
   // Location (Uri.base)
 
   var workingDirectory = environment["PWD"];
-  self.location = { href: "file://" + workingDirectory + "/" };
 
   // Global properties. "self" refers to the global object, so adding a
   // property to "self" defines a global variable.
   self.self = self;
+
+  self.location = { href: "file://" + workingDirectory + "/" };
+
+  // Support for deferred loading.
+  self.dartDeferredLibraryLoader = function(uri, successCallback, errorCallback) {
+    try {
+      load(uri);
+      successCallback();
+    } catch (error) {
+      errorCallback(error);
+    }
+  };
 })(this)
+
+var getKeys = function(obj){
+   var keys = [];
+   for(var key in obj){
+      keys.push(key);
+   }
+   return keys;
+}