Use a monotonic clock in the implementation of Timer.

runtime/bin/utils.h

 // 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.
 
 #ifndef BIN_UTILS_H_
 #define BIN_UTILS_H_
 
 #include <stdlib.h>
 #include <string.h>
 
@@ skipping 80 matching lines @@
   // Convert all the arguments to UTF8. On Windows, the arguments are
   // encoded in the current code page and not UTF8.
   //
   // Returns true if the arguments are converted. In that case
   // each of the arguments need to be deallocated using free.
   static bool GetUtf8Argv(int argc, char** argv);
 };
 
 class TimerUtils {
  public:
-  static int64_t GetCurrentTimeMicros();
-  static int64_t GetCurrentTimeMilliseconds();
+  static int64_t GetCurrentMonotonicMicros();
+  static int64_t GetCurrentMonotonicMillis();
   static void Sleep(int64_t millis);
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_UTILS_H_