util_test MachMessageServer.ReturnCodeNoReply: keep the child alive

until the server is done handling its request.

In most tests, this is handled automatically because the client expects
a reply from the server, and waits for this reply. This test is
different because the server does handle the message, but does not send
a reply, so the client does not wait for one. When the child process
exits before the parent has had a chance to inspect the message it
received, the parent will find a dead name where it expects the remote
port to be, causing this test to be flaky based on the outcome of this
race.

The potential for a similar race existed in the
MachMessageServer.ComplexNotDestroyedNoReply test because it also
involved a request without a reply. In that test, the situation was
handled by not allowing the child to exit until signaled to do so by the
parent. The same logic should be used for both no-reply tests.

TEST=util_test MachMessageServer.ReturnCodeNoReply
R=rsesek@chromium.org

Review URL: https://codereview.chromium.org/569953002

util/mach/mach_message_server_test.cc

@@ -685,6 +685,7 @@ TEST(MachMessageServer, ReturnCodeNoReply) {
   TestMachMessageServer::Options options;
   options.server_mig_retcode = MIG_NO_REPLY;
   options.client_expect_reply = false;
+  options.child_wait_for_parent_pipe = true;
   TestMachMessageServer test_mach_message_server(options);
   test_mach_message_server.Test();
 }