The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2a59ae081198c24539883b4f3c46d1752d8a317f

commit 2a59ae081198c24539883b4f3c46d1752d8a317f
Author: Istiaque Ahmed <lazyboy@chromium.org>
Date: Thu Aug 24 04:43:26 2017

Move ExternalTestingLoader out of production code.

Since this class it test only, it should live on test only target.
Move the class to extension_service_unittest.cc where it is used.

Bug:  758390 
Change-Id: Ide976029a6e561685082ff1d6dced83529a3077c
Reviewed-on: https://chromium-review.googlesource.com/630241
Commit-Queue: Istiaque Ahmed <lazyboy@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#496952}
[modify] https://crrev.com/2a59ae081198c24539883b4f3c46d1752d8a317f/chrome/browser/extensions/extension_service_unittest.cc
[modify] https://crrev.com/2a59ae081198c24539883b4f3c46d1752d8a317f/chrome/browser/extensions/external_pref_loader.cc
[modify] https://crrev.com/2a59ae081198c24539883b4f3c46d1752d8a317f/chrome/browser/extensions/external_pref_loader.h