Fix codegen and isolate issues for frog dart:html

frog/world.dart

Index: frog/world.dart
diff --git a/frog/world.dart b/frog/world.dart
index f7821a9fbc2735426c6422e137572ad63a38071c..9fe662c75ca3ab722f9a9e0ec1b487b6a3371254 100644
--- a/frog/world.dart
+++ b/frog/world.dart
@@ -104,6 +104,7 @@ class World {
 
   // TODO(jmesserly): we shouldn't be special casing DOM anywhere.
   Library dom;
+  Library html;
   Library isolatelib;
 
   List<Library> _todo;
@@ -472,6 +473,8 @@ class World {
 
       if (filename == 'dart:dom') {
         dom = library;
+      } else if (filename == 'dart:html') {
+        html = library;
       } else if (filename == 'dart:isolate') {
         isolatelib = library;
       }