I'd like to take over this bug.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e42008fc102f0f026efb181fd8e443d5d9c83df5

commit e42008fc102f0f026efb181fd8e443d5d9c83df5
Author: Gyuyoung Kim <gyuyoung@igalia.com>
Date: Wed Jan 16 14:03:43 2019

s13n: Remove an unnecessary SigninManager related include in chrome_extension_downloader_factory.cc

As a step to replace to IdentityManager, we don't need to include signin_manager.h here.

Bug:  920213 
Change-Id: I383756cbcc6442ca5faaab58b85a21a789e066eb
Reviewed-on: https://chromium-review.googlesource.com/c/1410732
Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Commit-Queue: Gyuyoung Kim <gyuyoung@igalia.com>
Cr-Commit-Position: refs/heads/master@{#623220}
[modify] https://crrev.com/e42008fc102f0f026efb181fd8e443d5d9c83df5/chrome/browser/extensions/updater/chrome_extension_downloader_factory.cc