We have a pattern of:
task_runner()->PostTask(
      FROM_HERE, base::BindOnce(&SomeClass::SomeFunction, GetWeakPtr())), where we expect to call callbacks inside SomeFunction.

However, if the weak pointer is invalidated before the callback is run, we may leave some callbacks uncalled, and therefore outstanding mojo calls may not be resolved, and promises may not resolve in blink.

Make a pass over where we do this to ensure we don't have bugs.  Add tests, and see if there are safer patterns.