Only return eventhandler tokens in stacks of 8, to avoid runtime calls.

runtime/bin/eventhandler_linux.cc

Index: runtime/bin/eventhandler_linux.cc
diff --git a/runtime/bin/eventhandler_linux.cc b/runtime/bin/eventhandler_linux.cc
index d44486ecf5cdf853527d60f4b7433808ebf896a8..763db7774ae1c520d1b7a847fc38b67f0c8d9437 100644
--- a/runtime/bin/eventhandler_linux.cc
+++ b/runtime/bin/eventhandler_linux.cc
@@ -209,8 +209,11 @@ void EventHandlerImplementation::HandleInterruptFd() {
         delete sd;
         DartUtils::PostInt32(msg[i].dart_port, 1 << kDestroyedEvent);
       } else if ((msg[i].data & (1 << kReturnTokenCommand)) != 0) {
-        if (sd->ReturnToken()) {
-          AddToEpollInstance(epoll_fd_, sd);
+        int count = msg[i].data & ((1 << kReturnTokenCommand) - 1);
+        for (int i = 0; i < count; i++) {
+          if (sd->ReturnToken()) {
+            AddToEpollInstance(epoll_fd_, sd);
+          }
         }
       } else {
         // Setup events to wait for.
@@ -275,7 +278,7 @@ void EventHandlerImplementation::HandleEvents(struct epoll_event* events,
       SocketData* sd = reinterpret_cast<SocketData*>(events[i].data.ptr);
       intptr_t event_mask = GetPollEvents(events[i].events, sd);
       if (event_mask != 0) {
-        if (sd->TakeToken()) {
+        if (!sd->IsListeningSocket() && sd->TakeToken()) {
           // Took last token, remove from epoll.
           RemoveFromEpollInstance(epoll_fd_, sd);
         }