Mojo cpp bindings: add support for validating incoming messages.

mojo/mojo_public.gypi

 {
   'targets': [
     {
       'target_name': 'mojo_system',
       'type': 'static_library',
       'defines': [
         'MOJO_SYSTEM_IMPLEMENTATION',
       ],
       'include_dirs': [
         '..',
@@ skipping 208 matching lines @@
       ],
       'sources': [
         'public/cpp/bindings/allocation_scope.h',
         'public/cpp/bindings/array.h',
         'public/cpp/bindings/buffer.h',
         'public/cpp/bindings/callback.h',
         'public/cpp/bindings/error_handler.h',
         'public/cpp/bindings/interface_impl.h',
         'public/cpp/bindings/interface_ptr.h',
         'public/cpp/bindings/message.h',
+        'public/cpp/bindings/message_filter.h',
         'public/cpp/bindings/no_interface.h',
         'public/cpp/bindings/passable.h',
         'public/cpp/bindings/sync_dispatcher.h',
         'public/cpp/bindings/type_converter.h',
         'public/cpp/bindings/lib/array.cc',
         'public/cpp/bindings/lib/array_internal.h',
         'public/cpp/bindings/lib/array_internal.cc',
         'public/cpp/bindings/lib/bindings_internal.h',
         'public/cpp/bindings/lib/bindings_serialization.cc',
         'public/cpp/bindings/lib/bindings_serialization.h',
         'public/cpp/bindings/lib/buffer.cc',
         'public/cpp/bindings/lib/callback_internal.h',
         'public/cpp/bindings/lib/connector.cc',
         'public/cpp/bindings/lib/connector.h',
+        'public/cpp/bindings/lib/filter_chain.cc',
+        'public/cpp/bindings/lib/filter_chain.h',
         'public/cpp/bindings/lib/fixed_buffer.cc',
         'public/cpp/bindings/lib/fixed_buffer.h',
         'public/cpp/bindings/lib/interface_impl_internal.h',
         'public/cpp/bindings/lib/interface_ptr_internal.h',
         'public/cpp/bindings/lib/message.cc',
         'public/cpp/bindings/lib/message_builder.cc',
         'public/cpp/bindings/lib/message_builder.h',
+        'public/cpp/bindings/lib/message_filter.cc',
         'public/cpp/bindings/lib/message_header_validator.cc',
         'public/cpp/bindings/lib/message_header_validator.h',
         'public/cpp/bindings/lib/message_internal.h',
         'public/cpp/bindings/lib/message_queue.cc',
         'public/cpp/bindings/lib/message_queue.h',
         'public/cpp/bindings/lib/no_interface.cc',
         'public/cpp/bindings/lib/router.cc',
         'public/cpp/bindings/lib/router.h',
         'public/cpp/bindings/lib/scratch_buffer.cc',
         'public/cpp/bindings/lib/scratch_buffer.h',
@@ skipping 124 matching lines @@
           'type': 'none',
           'variables': {
             'java_in_dir': 'public/java',
           },
           'includes': [ '../build/java.gypi' ],
         },
       ],
     }],
   ],
 }