Retrieve the list of keyboard layouts for public sessions async

Retrieve the list of keyboard layouts for public sessions async

CL 398543002 introduced a GetKeyboardLayoutsForLocale() method that
synchronous resolves the requested locale to an actually available UI
locale and returns the keyboard layouts available for it. However,
resolving a locale requires file I/O, which is not allowed on the UI
thread. This led to DCHECK failures.

This CL makes GetKeyboardLayoutsForLocale() asynchronous. It first
resolves the locale on a background thread and then retrieves the list
of keyboard layouts for it on the UI thread.

BUG=241790
TEST=Debug build no longer DCHECKs when choosing public session locale
R=alemate@chromium.org, dzhioev@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=286571

[bartfab (slow), 2014-07-25 16:07:11]

Hi Pavel,

Could you take a look?

[bartfab (slow), 2014-07-29 12:43:54]

Hi Pavel,

Friendly review ping.

[dzhioev (left Google), 2014-07-29 18:37:32]

LGTM

Alexander, can you please take a look?

[Nikita (slow), 2014-07-30 12:08:47]

https://codereview.chromium.org/417103003/diff/20001/chrome/browser/ui/webui/...
File chrome/browser/ui/webui/chromeos/login/l10n_util.cc (right):

https://codereview.chromium.org/417103003/diff/20001/chrome/browser/ui/webui/...
chrome/browser/ui/webui/chromeos/login/l10n_util.cc:445:
content::BrowserThread::FILE,
FILE thread is deprecated
https://groups.google.com/a/chromium.org/forum/#!msg/chromium-dev/OaA-9rnjOqI

[bartfab (slow), 2014-07-30 12:55:17]

https://codereview.chromium.org/417103003/diff/20001/chrome/browser/ui/webui/...
File chrome/browser/ui/webui/chromeos/login/l10n_util.cc (right):

https://codereview.chromium.org/417103003/diff/20001/chrome/browser/ui/webui/...
chrome/browser/ui/webui/chromeos/login/l10n_util.cc:445:
content::BrowserThread::FILE,
On 2014/07/30 12:08:47, Nikita Kostylev wrote:
> FILE thread is deprecated
> https://groups.google.com/a/chromium.org/forum/#!msg/chromium-dev/OaA-9rnjOqI

Done.

[Alexander Alekseev, 2014-07-30 14:34:02]

lgtm

[bartfab (slow), 2014-07-30 14:34:50]

The CQ bit was checked by bartfab@chromium.org

[commit-bot: I haz the power, 2014-07-30 14:35:48]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/bartfab@chromium.org/417103003/40001

[commit-bot: I haz the power, 2014-07-30 17:32:03]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_chromium_x64_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[bartfab (slow), 2014-07-30 19:04:44]

Committed patchset #3 manually as r286571 (presubmit successful).