Upstreaming browser/ui/uikit_ui_util from iOS.

Upstreaming browser/ui/uikit_ui_util from iOS.

Added AddSameCenterXConstraint which add constraints to a
parent view to horizontally align two subviews.
Added BOOL IsRTLUILayout() which take into account RTL pseudo
language. This will be removed once base::i18n::IsRTL() supports it.

BUG=None

Committed: https://crrev.com/18831714d344d489908705d374cf8c416afa603d
Cr-Commit-Position: refs/heads/master@{#342328}

[jbbegue, 2015-08-07 08:20:18]

jbbegue@chromium.org changed reviewers:
+ sdefresne@chromium.org

[sdefresne, 2015-08-07 10:07:13]

The CQ bit was checked by sdefresne@chromium.org

[sdefresne, 2015-08-07 10:07:13]

lgtm

[commit-bot: I haz the power, 2015-08-07 10:07:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1280913003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1280913003/1

[sdefresne, 2015-08-07 10:07:25]

Rubberstamp lgtm

[commit-bot: I haz the power, 2015-08-07 10:15:56]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-07 10:16:42]

Patchset 1 (id:??) landed as
https://crrev.com/18831714d344d489908705d374cf8c416afa603d
Cr-Commit-Position: refs/heads/master@{#342328}