Use a monotonic clock in the implementation of Timer.

runtime/bin/eventhandler_macos.cc

 // 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.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include "bin/eventhandler.h"
 #include "bin/eventhandler_macos.h"
 
@@ skipping 376 matching lines @@
     HandleInterruptFd();
   }
 }
 
 
 int64_t EventHandlerImplementation::GetTimeout() {
   if (!timeout_queue_.HasTimeout()) {
     return kInfinityTimeout;
   }
   int64_t millis = timeout_queue_.CurrentTimeout() -
-      TimerUtils::GetCurrentTimeMilliseconds();
+      TimerUtils::GetCurrentMonotonicMillis();
   return (millis < 0) ? 0 : millis;
 }
 
 
 void EventHandlerImplementation::HandleTimeout() {
   if (timeout_queue_.HasTimeout()) {
     int64_t millis = timeout_queue_.CurrentTimeout() -
-        TimerUtils::GetCurrentTimeMilliseconds();
+        TimerUtils::GetCurrentMonotonicMillis();
     if (millis <= 0) {
       DartUtils::PostNull(timeout_queue_.CurrentPort());
       timeout_queue_.RemoveCurrent();
     }
   }
 }
 
 
 void EventHandlerImplementation::EventHandlerEntry(uword args) {
   static const intptr_t kMaxEvents = 16;
@@ skipping 65 matching lines @@
 
 uint32_t EventHandlerImplementation::GetHashmapHashFromFd(intptr_t fd) {
   // The hashmap does not support keys with value 0.
   return dart::Utils::WordHash(fd + 1);
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)