Add Timer implementation for dart2js. Also moves tests to appropriate location.

lib/isolate/dart2js/compiler_hooks.dart

Index: lib/isolate/dart2js/compiler_hooks.dart
diff --git a/lib/isolate/dart2js/compiler_hooks.dart b/lib/isolate/dart2js/compiler_hooks.dart
index 23759fa85631a4f97c4e2a4c9e9677855f0fcda8..052928a0db926e6c803d480f83ef57fee4ec6530 100644
--- a/lib/isolate/dart2js/compiler_hooks.dart
+++ b/lib/isolate/dart2js/compiler_hooks.dart
@@ -27,6 +27,9 @@ void startRootIsolate(entry) {
   // by having a "default" isolate (the first one created).
   _globalState.currentContext = rootContext;
 
+  if (_window != null)  {
+    rootContext.eval(() => _setTimerFactoryClosure( _timerFactory));
+  }
   rootContext.eval(entry);
   _globalState.topEventLoop.run();
 }