Merge the Sky Engine changes from the SkyDart branch

sky/tests/lowlevel/home.sky

 <div>
 <style>
  .h1 { font-size: 2em; margin: 1em; }
  .p { margin: 0.5em 1em; color: #bcd8f5; font-weight: 900; }
 </style>
 <div class="h1">about:blank</div>
 <div class="p">Welcome to Sky!</div>
 <script>
+import "dart:sky" as sky;
+import "dart:sky.internals" as internals;
+
 // Don't use dump-as-render-tree.sky, we want a test with no imports.
-window.addEventListener('load', function() {
-  internals.notifyTestComplete(internals.renderTreeAsText());
-});
+void main() {
+  sky.window.addEventListener('load', (_) =>
+    internals.notifyTestComplete(internals.renderTreeAsText()));  
+}
 </script>
 </div>