Mojo cpp bindings: add support for validating incoming messages.

mojo/public/cpp/bindings/message.h

Index: mojo/public/cpp/bindings/message.h
diff --git a/mojo/public/cpp/bindings/message.h b/mojo/public/cpp/bindings/message.h
index 5653f05eb6022aaeeeb9e9a8bff1257fb5a6854e..e6c42058ac23d34c5183d1ccfc45e9e2fcb5e496 100644
--- a/mojo/public/cpp/bindings/message.h
+++ b/mojo/public/cpp/bindings/message.h
@@ -103,6 +103,8 @@ class MessageReceiver {
 // Returns MOJO_RESULT_SHOULD_WAIT if the caller should wait on the handle to
 // become readable. Returns MOJO_RESULT_OK if a message was dispatched and
 // otherwise returns an error code if something went wrong.
+//
+// NOTE: The message hasn't been validated and may be malformed!
 MojoResult ReadAndDispatchMessage(MessagePipeHandle handle,
                                   MessageReceiver* receiver,
                                   bool* receiver_result);