First step towards support for being able to interrupt a running Dart Isolate

runtime/bin/dbg_connection_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 <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/event.h>
 #include <unistd.h>
@@ skipping 66 matching lines @@
 
     /* For now, don't poll the debugger connection.
     struct kevent ev_add;
     EV_SET(&ev_add, fd, EVFILT_READ, EV_ADD, 0, 0, NULL);
     int status =
         TEMP_FAILURE_RETRY(kevent(kqueue_fd_, &ev_add, 1, NULL, 0, NULL));
     if (status == -1) {
       FATAL1("Failed adding debugger socket to kqueue: %s\n", strerror(errno));
     }
     */
-  } else if (ident == DebuggerConnectionHandler::debugger_fd_) {
-    printf("unexpected: receiving debugger connection event.\n");
-    UNIMPLEMENTED();
-  } else {
+  } else if (ident == wakeup_fds[0]) {
     Message msg;
     if (ReceiveMessage(&msg)) {
       printf("Received sync message id %d.\n", msg.msg_id);
     }
+  } else {
+    printf("unexpected: receiving debugger connection event.\n");
+    UNIMPLEMENTED();
   }
 }
 
 
 void DebuggerConnectionImpl::Handler(uword args) {
   static const intptr_t kMaxEvents = 4;
   struct kevent events[kMaxEvents];
 
   while (1) {
     // Wait indefinitely for an event.
@@ skipping 44 matching lines @@
 
 void DebuggerConnectionImpl::StartHandler(int port_number) {
   ASSERT(DebuggerConnectionHandler::listener_fd_ != -1);
   SetupPollQueue();
   int result =
       dart::Thread::Start(&DebuggerConnectionImpl::Handler, 0);
   if (result != 0) {
     FATAL1("Failed to start debugger connection handler thread: %d\n", result);
   }
 }