Simplify mojo_shell since it's now only used for Mandoline.

mojo/application/application_test_main_chromium.cc

 // 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.
 
 #include "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/test/test_timeouts.h"
+#include "mojo/application/application_test_base_chromium.h"
 #include "mojo/public/c/system/main.h"
-#include "mojo/public/cpp/application/application_test_base.h"
 
 MojoResult MojoMain(MojoHandle handle) {
   // An AtExitManager instance is needed to construct message loops.
   base::AtExitManager at_exit;
 
   // Initialize test timeouts, which requires CommandLine::ForCurrentProcess().
   // TODO(msw): Plumb relevant command line args before initializing timeouts.
   base::CommandLine::Init(0, nullptr);
   TestTimeouts::Initialize();
 
   return mojo::test::RunAllTests(handle);
 }