This is a duplicate of the  issue 872778  if I understand your description correctly.

Actually not, this issue was created because of the fix for  crbug.com/872778  :)

The fix for 872778 adds brokered creation methods to mojo, and adds comments to base referring to mojo.

This bug is a possible next step, to add hooks to base so that brokering can be done directly.

I personally think this is going to be hard in practice: most brokering implementations are going to use mojo, and so this will end up adding a practical dependency on mojo anyway.

But I have to think about it more.

I think it's OK if the injected implementation depends on Mojo. The point of this is so that individual callers can have a consistent interface to create shared memory, rather than having to remember to sometimes go through Mojo. The consistent interface will Just Work because the bootstrap process should configure the hooks as needed for a given process type.