Support for a dart2js `dartDeferredLoader` hook.

sdk/lib/_internal/compiler/js_lib/preambles/d8.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 V8's d8 shell.
 
 // Node wraps files and provides them with a different `this`. The global
 // `this` can be accessed through `global`.
 
 var self = this;
 if (typeof global != "undefined") self = global;  // Node.js.
@@ skipping 250 matching lines @@
         } else {
           throw e;
         }
       }
       action = nextEvent();
     }
   }
 
   // Global properties. "self" refers to the global object, so adding a
   // property to "self" defines a global variable.
+  self.self = self
   self.dartMainRunner = function(main, args) {
     // Initialize.
     var action = function() { main(args); }
     eventLoop(action);
   };
   self.setTimeout = addTimer;
   self.clearTimeout = cancelTimer;
   self.setInterval = addInterval;
   self.clearInterval = cancelTimer;
   self.scheduleImmediate = addTask;
-  self.self = self;
+
+  // Support for deferred loading.
+  self.dartDeferredLibraryLoader = function(uri, successCallback, errorCallback) {
+    try {
+      load(uri);
+      successCallback();
+    } catch (error) {
+      errorCallback(error);
+    }
+  };
 })(self);