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

runtime/bin/dbg_connection_macos.cc

Index: runtime/bin/dbg_connection_macos.cc
===================================================================
--- runtime/bin/dbg_connection_macos.cc	(revision 12932)
+++ runtime/bin/dbg_connection_macos.cc	(working copy)
@@ -84,14 +84,14 @@
       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();
   }
 }