Let me take over this bug.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/81cd63979e7fb20cbc42824992cde618a04941d8

commit 81cd63979e7fb20cbc42824992cde618a04941d8
Author: Gyuyoung Kim <gyuyoung@igalia.com>
Date: Wed Jan 16 09:35:12 2019

s13n: Remove SigninManager-related includes from identity_apitest.cc

This CL cleans up the unnecessary includes related to SigninManager.

Bug:  920210 
Change-Id: I67b9505ad35270ca50356dade8e02fb478557000
Reviewed-on: https://chromium-review.googlesource.com/c/1414730
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Commit-Queue: Gyuyoung Kim <gyuyoung@igalia.com>
Cr-Commit-Position: refs/heads/master@{#623173}
[modify] https://crrev.com/81cd63979e7fb20cbc42824992cde618a04941d8/chrome/browser/extensions/api/identity/identity_apitest.cc