Fix invalid cast in AutofillDialogControllerTest.

An instance of autofill::AutofillDialogControllerImpl was converted
to its base class, TestAutofillDialogController to bypass protected
modifier on view(). This invalid case was found by CFI check:

https://www.chromium.org/developers/testing/control-flow-integrity

BUG=569102

Review URL: https://codereview.chromium.org/1515293003

Cr-Commit-Position: refs/heads/master@{#364872}
2 files changed