Currently there are many places that null callbacks can be passed, therefore, in some code, especially test code, we need to pass in a null callback. Currently this can be done by creating an null/empty callback directly, but there are two minor issues:
1. The callback name can be long, e.g. AudioDecoder::WaitingForDecryptionKeyCB()
2. It's harder to read. To me it's not super intuitive that a default constructed object is a null object.
I am proposing to introduce a base::NullCallback which can be implicitly converted to any null callback, similar to how base::DoNothing works.
Comment 1 by xhw...@chromium.org
, May 11 2018