The current mechanism of filling on account select is the following (see password_controller.mm and autofill_agent.mm for details):

1.checkIfSuggestionsAvailableForForm is called, which returns whether suggestions available.
2.retrieveSuggestionsForForm is called for getting suggestions.

Both functions have the same arguments and similar logic. retrieveSuggestionsForForm is called if checkIfSuggestionsAvailableForForm returns true. So checkIfSuggestionsAvailableForForm may be removed and retrieveSuggestionsForForm will check whether suggestions available and return them.