Mojo cpp bindings: add support for validating incoming messages.

mojo/mojo_public.gypi

Index: mojo/mojo_public.gypi
diff --git a/mojo/mojo_public.gypi b/mojo/mojo_public.gypi
index 65102eb67538f6e8df6c77c62cedb4874bfc5c0a..4988df3c17f9503c9bd19f0a77b5a5fede4fd861 100644
--- a/mojo/mojo_public.gypi
+++ b/mojo/mojo_public.gypi
@@ -226,6 +226,7 @@
         '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',
@@ -240,6 +241,8 @@
         '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',
@@ -247,6 +250,7 @@
         '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',