Working on this

Yesterday the only test using it was removed in crrev.com/c/1346400. I noticed after uploading a CL fixing it. Will use it anyway to remove the leftover includes.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/310bb6399810687c96d9ef9dce64068c7b3865c1

commit 310bb6399810687c96d9ef9dce64068c7b3865c1
Author: Sergio Villar Senin <svillar@igalia.com>
Date: Wed Nov 28 17:16:37 2018

Remove leftover includes in safe_browsing_blocking_page_unittest.cc

It was using the SigninManager API, but the only test using it was
removed in crrev.com/c/1346400. Just removing the leftover includes.

Bug:  903881 
Change-Id: Idb35dbff7a1b4f1d48140f4d2a6955cc8788dc63
Reviewed-on: https://chromium-review.googlesource.com/c/1352423
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Sergio Villar <svillar@igalia.com>
Cr-Commit-Position: refs/heads/master@{#611746}
[modify] https://crrev.com/310bb6399810687c96d9ef9dce64068c7b3865c1/chrome/browser/safe_browsing/safe_browsing_blocking_page_unittest.cc