Shutdown the sandbox MessageServer before deleting it.

sandbox/mac/mach_message_server.cc

Index: sandbox/mac/mach_message_server.cc
diff --git a/sandbox/mac/mach_message_server.cc b/sandbox/mac/mach_message_server.cc
index 20bd94c21f50e5d89e5ed82f8056562f95733eaf..7626c3af545336a73c5c96114bc4e80899183d45 100644
--- a/sandbox/mac/mach_message_server.cc
+++ b/sandbox/mac/mach_message_server.cc
@@ -76,6 +76,10 @@ bool MachMessageServer::Initialize() {
   return true;
 }
 
+void MachMessageServer::Shutdown() {
+  dispatch_source_.reset();
+}
+
 pid_t MachMessageServer::GetMessageSenderPID(IPCMessage request) {
   // Get the PID of the task that sent this request. This requires getting at
   // the trailer of the message, from the header.