Fix errors in Sky detected by Dart analyzer

sky/examples/fn/lib/fakesky.dart

 import 'dart:async';
 
 void assertHasParentNode(Node n) { assert(n.parentNode != null); }
 void assertHasParentNodes(List<Node> list) {
   for (var n in list) {
     assertHasParentNode(n);
   }
 }
 
 class Node {
@@ skipping 99 matching lines @@
   Document();
   Element createElement(String tagName) {
     switch (tagName) {
       case 'img' : return new HTMLImageElement();
       default : return new Element();
     }
   }
 }
 
 class HTMLImageElement extends Element {
-  Image();
+  HTMLImageElement();
   String src;
   Object style = {};
 }
 
 class Event {}
 
 class PointerEvent extends Event {}
 class GestureEvent extends Event {}
 class WheelEvent extends Event {}
 
 typedef EventListener(Event event);
 
 void _callRAF(Function fn) {
   fn(new DateTime.now().millisecondsSinceEpoch.toDouble());
 }
 
 class Window {
   int requestAnimationFrame(Function fn) {
     new Timer(const Duration(milliseconds: 16), () {
       _callRAF(fn);
     });
+    return 1;
   }
 
   void cancelAnimationFrame(int id) {
   }
 }
 
 Document document = new Document();
 
 Window window = new Window();
 
 class ClientRect {
-    double top
+    double top;
     double right;
     double bottomr;
     double left;
     double width;
     double height;
 }