Mojo: Move message pipe types/constants/functions from mojo/public/c/system/core.h to .../message_p…

mojo/mojo_public.gypi

 {
   'targets': [
     {
       'target_name': 'mojo_system',
       'type': 'static_library',
       'defines': [
         'MOJO_SYSTEM_IMPLEMENTATION',
       ],
       'include_dirs': [
         '..',
@@ skipping 11 matching lines @@
             'ldflags!': [
               '-Wl,--exclude-libs=ALL',
             ],
           }],
         ],
       },
       'sources': [
         'public/c/system/core.h',
         'public/c/system/functions.h',
         'public/c/system/macros.h',
+        'public/c/system/message_pipe.h',
         'public/c/system/system_export.h',
         'public/c/system/types.h',
         'public/platform/native/system_thunks.cc',
         'public/platform/native/system_thunks.h',
       ],
     },
     {
       'target_name': 'mojo_gles2',
       'type': 'shared_library',
       'defines': [
@@ skipping 377 matching lines @@
           },
           'dependencies': [
             'mojo_public_java',
           ],
           'includes': [ '../build/java.gypi' ],
         },
       ],
     }],
   ],
 }