Add Chromium environment application test support.

mojo/public/cpp/application/lib/application_test_main.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 "mojo/public/c/system/main.h"
 #include "mojo/public/cpp/application/application_delegate.h"
 #include "mojo/public/cpp/application/application_impl.h"
 #include "mojo/public/cpp/application/application_test_base.h"
 #include "mojo/public/cpp/environment/logging.h"
 #include "mojo/public/cpp/system/message_pipe.h"
 
 MojoResult MojoMain(MojoHandle shell_handle) {
+  // An Environment instance is needed to construct run loops.
   mojo::Environment environment;
 
   {
     // This RunLoop is used for init, and then destroyed before running tests.
     mojo::Environment::InstantiateDefaultRunLoop();
 
     // Construct an ApplicationImpl just for the GTEST commandline arguments.
     // GTEST command line arguments are supported amid application arguments:
     // $ mojo_shell 'mojo:example_apptest arg1 --gtest_filter=foo arg2'
     mojo::ApplicationDelegate dummy_application_delegate;
@@ skipping 18 matching lines @@
   }
 
   int result = RUN_ALL_TESTS();
 
   shell_handle = mojo::test::PassShellHandle().release().value();
   MojoResult close_result = MojoClose(shell_handle);
   MOJO_CHECK(close_result == MOJO_RESULT_OK);
 
   return (result == 0) ? MOJO_RESULT_OK : MOJO_RESULT_UNKNOWN;
 }