Move unittest from lib to pkg.

tests/html/window_open_test.dart

 #library('WindowOpenTest');
-#import('../../lib/unittest/unittest.dart');
-#import('../../lib/unittest/html_config.dart');
+#import('../../pkg/unittest/unittest.dart');
+#import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
   evaluateJavaScript(code) {
     final scriptTag = new Element.tag('script');
     scriptTag.innerHTML = code;
     document.body.nodes.add(scriptTag);
   }
   evaluateJavaScript('layoutTestController.setCanOpenWindows()');
 
@@ skipping 10 matching lines @@
 
 closeWindow(win) {
   win.close();
   doneHandler() {
     if (!win.closed) {
       window.setTimeout(expectAsync0(doneHandler), 1);
     }
   }
   window.setTimeout(expectAsync0(doneHandler), 1);
 }