Use a monotonic clock in the implementation of Timer.

runtime/bin/eventhandler.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 "bin/dartutils.h"
 #include "bin/eventhandler.h"
 #include "bin/lockers.h"
 #include "bin/socket.h"
 #include "bin/thread.h"
 
@@ skipping 113 matching lines @@
   Dart_Port dart_port;
   handle = Dart_SendPortGetId(handle, &dart_port);
   if (Dart_IsError(handle)) {
     Dart_PropagateError(handle);
     UNREACHABLE();
   }
   int64_t data = DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 2));
   event_handler->SendData(id, dart_port, data);
 }
 
+
+void FUNCTION_NAME(EventHandler_TimerMillisecondClock)(
+    Dart_NativeArguments args) {
+  int64_t now = TimerUtils::GetCurrentMonotonicMillis();
+  Dart_SetReturnValue(args, Dart_NewInteger(now));
+}
+
 }  // namespace bin
 }  // namespace dart