Mojo: Factor MessageInTransit secondary buffer stuff out into a separate class.

mojo/mojo.gyp

 # Copyright 2013 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.
 
 {
   'target_defaults': {
     'conditions': [
       ['mojo_shell_debug_url != ""', {
         'defines': [
           'MOJO_SHELL_DEBUG=1',
@@ skipping 174 matching lines @@
         'system/raw_channel_posix.cc',
         'system/raw_channel_win.cc',
         'system/raw_shared_buffer.cc',
         'system/raw_shared_buffer.h',
         'system/raw_shared_buffer_posix.cc',
         'system/raw_shared_buffer_win.cc',
         'system/shared_buffer_dispatcher.cc',
         'system/shared_buffer_dispatcher.h',
         'system/simple_dispatcher.cc',
         'system/simple_dispatcher.h',
+        'system/transport_data.cc',
+        'system/transport_data.h',
         'system/waiter.cc',
         'system/waiter.h',
         'system/waiter_list.cc',
         'system/waiter_list.h',
         # Test-only code:
         # TODO(vtl): It's a little unfortunate that these end up in the same
         # component as non-test-only code. In the static build, this code should
         # hopefully be dead-stripped.
         'embedder/test_embedder.cc',
         'embedder/test_embedder.h',
@@ skipping 606 matching lines @@
             'mojo_js_unittests.isolate',
           ],
           'sources': [
             'mojo_js_unittests.isolate',
           ],
         },
       ],
     }],
   ],
 }