Add Chromium environment application test support.

mojo/application/application_test_main_chromium.cc

Index: mojo/application/application_test_main_chromium.cc
diff --git a/mojo/public/cpp/application/lib/application_test_main.cc b/mojo/application/application_test_main_chromium.cc
similarity index 92%
copy from mojo/public/cpp/application/lib/application_test_main.cc
copy to mojo/application/application_test_main_chromium.cc
index be4e54ef1125c371740cfc3210be9f818919849b..0502689ac4b771d47e1f68a45b92ca065d1d43e8 100644
--- a/mojo/public/cpp/application/lib/application_test_main.cc
+++ b/mojo/application/application_test_main_chromium.cc
@@ -2,6 +2,7 @@
 // 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 "mojo/public/c/system/main.h"
 #include "mojo/public/cpp/application/application_delegate.h"
 #include "mojo/public/cpp/application/application_impl.h"
@@ -10,7 +11,10 @@
 #include "mojo/public/cpp/system/message_pipe.h"
 
 MojoResult MojoMain(MojoHandle shell_handle) {
-  mojo::Environment environment;
+#if !defined(COMPONENT_BUILD)
+  // An AtExitManager instance is needed to construct message loops.
+  base::AtExitManager at_exit;
+#endif
 
   {
     // This RunLoop is used for init, and then destroyed before running tests.