Rename Timer.repeating to Timer.periodic.

tests/html/async_window_test.dart

 library AsyncWindowTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 import 'dart:async';
 
 main() {
   useHtmlConfiguration();
   test('Timer', () {
     new Timer(const Duration(milliseconds: 10), expectAsync0((){}));
   });
-  test('Timer.repeating', () {
+  test('Timer.periodic', () {
     int counter = 0;
     int id = null;
-    new Timer.repeating(const Duration(milliseconds: 10),
+    new Timer.periodic(const Duration(milliseconds: 10),
         expectAsyncUntil1(
         (timer) {
           if (counter == 3) {
             counter = 1024;
             timer.cancel();
             // Wait some more time to be sure callback won't be invoked any
             // more.
             new Timer(const Duration(milliseconds: 50), expectAsync0((){}));
             return;
           }
           // As callback should have been cleared on 4th invocation, counter
           // should never be greater than 3.
           assert(counter < 3);
           counter++;
         },
         () => counter == 3));
   });
 }