Fix more lint style issues in runtime patches.

runtime/lib/timer_patch.dart

 // Copyright (c) 2012, 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:_internal' hide Symbol;
+
 @patch class Timer {
   @patch static Timer _createTimer(Duration duration, void callback()) {
     // TODO(iposva): Remove _TimerFactory and use VMLibraryHooks exclusively.
     if (_TimerFactory._factory == null) {
       _TimerFactory._factory = VMLibraryHooks.timerFactory;
     }
     if (_TimerFactory._factory == null) {
       throw new UnsupportedError("Timer interface not supported.");
     }
     int milliseconds = duration.inMilliseconds;
@@ skipping 18 matching lines @@
 
 typedef Timer _TimerFactoryClosure(int milliseconds,
                                    void callback(Timer timer),
                                    bool repeating);
 
 // Warning: Dartium sets _TimerFactory._factory instead of setting things up
 // through VMLibraryHooks.timerFactory.
 class _TimerFactory {
   static _TimerFactoryClosure _factory;
 }