Use a monotonic clock in the implementation of Timer.

runtime/bin/eventhandler_android.cc

Index: runtime/bin/eventhandler_android.cc
diff --git a/runtime/bin/eventhandler_android.cc b/runtime/bin/eventhandler_android.cc
index 14cddc1554b13339e9fa625e5db645b1ae413607..6fdabfb9fae87e25c972ab2703f45fb45e65f890 100644
--- a/runtime/bin/eventhandler_android.cc
+++ b/runtime/bin/eventhandler_android.cc
@@ -333,7 +333,7 @@ int64_t EventHandlerImplementation::GetTimeout() {
     return kInfinityTimeout;
   }
   int64_t millis = timeout_queue_.CurrentTimeout() -
-      TimerUtils::GetCurrentTimeMilliseconds();
+      TimerUtils::GetCurrentMonotonicMillis();
   return (millis < 0) ? 0 : millis;
 }
 
@@ -341,7 +341,7 @@ int64_t EventHandlerImplementation::GetTimeout() {
 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();