[Signin] Dummy Reauth API

This CL adds a new method ShowReauthPrompt() to SigninViewController.

The callers cannot rely on Reauth prompt being displayed in a modal
dialog, since for some accounts Reauth is always shown in a popup
window.

Bug: 1045515
Change-Id: Ida343ffae2cff59b51f4b4c7f12b1e27db3b8297
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2020764
Commit-Queue: Alex Ilin <[email protected]>
Reviewed-by: David Roger <[email protected]>
Cr-Commit-Position: refs/heads/master@{#736516}
4 files changed