Make GlobalDescriptors::MaybeGet return -1 when the key is not found.

ipc/sync_socket_unittest.cc

Index: ipc/sync_socket_unittest.cc
diff --git a/ipc/sync_socket_unittest.cc b/ipc/sync_socket_unittest.cc
index 6aa33306d9cbab13baec13dff2dd7453bc9987ba..c8c81879735f74afc6957b2e3b67c9424008c539 100644
--- a/ipc/sync_socket_unittest.cc
+++ b/ipc/sync_socket_unittest.cc
@@ -13,6 +13,7 @@
 #include "base/process_util.h"
 #include "base/threading/thread.h"
 #include "ipc/ipc_channel_proxy.h"
+#include "ipc/ipc_multiprocess_test.h"
 #include "ipc/ipc_tests.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/multiprocess_func_list.h"
@@ -108,7 +109,7 @@ class SyncSocketServerListener : public IPC::Channel::Listener {
 
 // Runs the fuzzing server child mode. Returns when the preset number
 // of messages have been received.
-MULTIPROCESS_TEST_MAIN(RunSyncSocketServer) {
+MULTIPROCESS_IPC_TEST_MAIN(RunSyncSocketServer) {
   MessageLoopForIO main_message_loop;
   SyncSocketServerListener listener;
   IPC::Channel chan(kSyncSocketChannel, IPC::Channel::MODE_CLIENT, &listener);