Replace ChildProcess/AppChildProcess with a simple ChildMain().

shell/child_main.h

+// Copyright 2014 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 SHELL_CHILD_MAIN_H_
+#define SHELL_CHILD_MAIN_H_
+
+namespace mojo {
+namespace shell {
+
+// The "main()" for child processes. This should be called with a
+// the |base::CommandLine| singleton initialized and a |base::AtExitManager|,
+// but without a |base::MessageLoop| for the current thread. Returns the exit
+// code for the process.
+int ChildMain();
+
+}  // namespace shell
+}  // namespace mojo
+
+#endif  // SHELL_CHILD_MAIN_H_