Copy lib/dom tests that use dart:html to lib/html.

tests/dom/performance_api_test.dart

-#library('PerformanceApiTest');
-#import('../../lib/unittest/unittest.dart');
-#import('../../lib/unittest/html_config.dart');
-#import('dart:html');
-
-main() {
-  useHtmlConfiguration();
-  test('PerformanceApi', () {
-    // Check that code below will not throw exceptions.
-    var requestStart = window.performance.timing.requestStart;
-    var responseStart = window.performance.timing.responseStart;
-    var responseEnd = window.performance.timing.responseEnd;
-    
-    var loading = window.performance.timing.domLoading;
-    var loadedStart = window.performance.timing.domContentLoadedEventStart;
-    var loadedEnd = window.performance.timing.domContentLoadedEventEnd;
-    var complete = window.performance.timing.domComplete;
-
-    var loadEventStart = window.performance.timing.loadEventStart;
-  });
-}