Reverted in https://codereview.chromium.org/2146573005/.

Fixing the underlying issue in https://codereview.chromium.org/2150583002 before relanding

#2: so this issue is unrelated to  issue 624446 ? ArcAppModelBuilderTest.RequestShortcutIcons is flaky with a similar stack trace.

Oh they might be related. I'll take a look and see if I can fix that and reenable it while I'm at it.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4303e815b33c5d970e210ca9edd2b6bafedc8ad3

commit 4303e815b33c5d970e210ca9edd2b6bafedc8ad3
Author: lhchavez <lhchavez@chromium.org>
Date: Fri Jul 15 00:04:00 2016

Fix ArcAppModelBuilderTest

Several tests in this suite were flaky. This change:

* Sets up a real I/O thread for the ExtensionsService and
  sets the profile mapping in case the garbage collector
  kicks in.
* Does a better job of waiting for the icons to be loaded.
* Uniformly disables safe icon decoding since it introduces
  extra thread hops that are difficult to synchronize for.

BUG= 627853 
BUG= 624446 
TEST=./unit_tests --gtest-filter=ArcAppModelBuilderTest*
TEST=for each test:
     ./unit_tests --gtest-filter=${t} --single-process-tests

Review-Url: https://codereview.chromium.org/2150583002
Cr-Commit-Position: refs/heads/master@{#405643}

[modify] https://crrev.com/4303e815b33c5d970e210ca9edd2b6bafedc8ad3/chrome/browser/chromeos/profiles/profile_helper.h
[modify] https://crrev.com/4303e815b33c5d970e210ca9edd2b6bafedc8ad3/chrome/browser/ui/app_list/app_list_test_util.cc
[modify] https://crrev.com/4303e815b33c5d970e210ca9edd2b6bafedc8ad3/chrome/browser/ui/app_list/arc/arc_app_test.cc
[modify] https://crrev.com/4303e815b33c5d970e210ca9edd2b6bafedc8ad3/chrome/browser/ui/app_list/arc/arc_app_test.h
[modify] https://crrev.com/4303e815b33c5d970e210ca9edd2b6bafedc8ad3/chrome/browser/ui/app_list/arc/arc_app_unittest.cc