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

ipc/ipc_multiprocess_test.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IPC_IPC_MULTIPROCESS_TEST_H_
+#define IPC_IPC_MULTIPROCESS_TEST_H_
+#pragma once
+
+#include "base/test/multiprocess_test.h"
+
+// Use this macro when your sub-process is using an IPCChannel to communicate
+// with the test process.
+// See comment below for MultiProcessTestIPCSetUp() on why this is needed.
+#define MULTIPROCESS_IPC_TEST_MAIN(test_main) \
+  MULTIPROCESS_TEST_MAIN_WITH_SETUP(test_main, MultiProcessTestIPCSetUp)
+
+// Setup function used by MULTIPROCESS_IPC_TEST_MAIN.
+// Registers the IPC channel as a global descriptor in the child process. This
+// is needed on POSIX as the IPCChannel when created looks for a specific global
+// descriptor to establish the connection to the parent process.
+void MultiProcessTestIPCSetUp();
+
+#endif  // IPC_IPC_MULTIPROCESS_TEST_H_