fixes #168, dart:js implementation with a test

test/codegen/expect/sunflower/dom.js

Index: test/codegen/expect/sunflower/dom.js
diff --git a/test/codegen/expect/sunflower/dom.js b/test/codegen/expect/sunflower/dom.js
index 51474927d0c14aba5e05120841152cbb4f401862..92d43893d6fea5ec0038e4199820a5acd8919f2f 100644
--- a/test/codegen/expect/sunflower/dom.js
+++ b/test/codegen/expect/sunflower/dom.js
@@ -22,9 +22,19 @@ dart_library.library('dom', window, /* Imports */[
     constructors: () => ({Overload: [Overload, []]})
   });
   let overload = dart.const(new Overload());
+  class CustomEvent extends core.Object {}
+  dart.setSignature(CustomEvent, {
+    constructors: () => ({CustomEvent: [CustomEvent, [core.String], {detail: dart.dynamic, bubbles: dart.dynamic, cancelable: dart.dynamic}]})
+  });
+  class HTMLCollection extends core.Object {}
+  dart.setSignature(HTMLCollection, {
+    methods: () => ({get: [Element, [core.num]]})
+  });
   let EventListener = dart.typedef('EventListener', () => dart.functionType(dart.void, [Event]));
   let InputElement = HTMLInputElement;
   let CanvasElement = HTMLCanvasElement;
+  let DivElement = HTMLDivElement;
+  let ScriptElement = HTMLScriptElement;
   class RenderingContext extends core.Object {}
   class CanvasDrawingStyles extends core.Object {
     CanvasDrawingStyles() {
@@ -43,9 +53,13 @@ dart_library.library('dom', window, /* Imports */[
   exports.JsName = JsName;
   exports.Overload = Overload;
   exports.overload = overload;
+  exports.CustomEvent = CustomEvent;
+  exports.HTMLCollection = HTMLCollection;
   exports.EventListener = EventListener;
   exports.InputElement = InputElement;
   exports.CanvasElement = CanvasElement;
+  exports.DivElement = DivElement;
+  exports.ScriptElement = ScriptElement;
   exports.RenderingContext = RenderingContext;
   exports.CanvasDrawingStyles = CanvasDrawingStyles;
   exports.CanvasPathMethods = CanvasPathMethods;