SimpleWebViewDialog does not create an AutofillClient, so PasswordAutofillManager ends up with a null |autofill_client_|.

SimpleWebViewDialog doesn't seem to trigger any code paths in PasswordAutofillManager that use |autofill_client_| except for OnShowNotSecureWarning().

We temporarily added a null check to OnShowNotSecureWarning in https://codereview.chromium.org/2733043005/, but that doesn't seem like the right solution. We could instead create an AutofillClient for SimpleWebViewDialog to use, but that triggers other crashes (see https://codereview.chromium.org/2727813006/#msg15). We should figure out if it's possible to use the password_manager component with SimpleWebViewDialog for FNS warnings and if so, re-enable OnShowNotSecureWarning for this case.