Split dart:builtin into dart:builtin and dart:io.

tests/standalone/src/TimerCancelTest.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+#import("dart:io");
+
 class TimerCancelTest {
 
   static void testSimpleTimer() {
 
     void timeoutHandlerUnreachable(Timer timer) {
       Expect.equals(true, false);
     }
 
     void timeoutHandler(Timer timer) {
       cancelTimer.cancel();
@@ skipping 17 matching lines @@
     testSimpleTimer();
   }
 
   static Timer cancelTimer;
   static int repeatTimer;
 }
 
 main() {
   TimerCancelTest.testMain();
 }