Use different Access Point on iOS for phone and tablet

Use different Access Point on iOS for phone and tablet

Introduce an accessor for the value of the access point since it is no
longer a constant for the platform but may depends on conditions that
are only known at runtime (difference between phone and tablet on iOS).

Chrome on iOS will use the access point C9 and CD for tracking usage of
the omnibox on tablet and phone respectively.

BUG=375170
TBR=thakis

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=272124

[sdefresne, 2014-05-20 16:32:34]

rogerta: chrome/browser/rlz & rlz/, please review the API change that are
required due to the iOS requirement (ie. different AP for tablet / phone)

thakis: TBR for OWNERS of chrome/browser/{chromeos,search_engines,ui} (change of
API that is reported to client code)

[Roger Tawa OOO till Jul 10th, 2014-05-20 19:06:49]

lgtm

[Nico, 2014-05-20 21:52:48]

lgtm

[sdefresne, 2014-05-21 07:51:29]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2014-05-21 07:54:15]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/sdefresne@chromium.org/292983003/1

[commit-bot: I haz the power, 2014-05-22 05:28:52]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  android_dbg_triggered_tests on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/android_dbg_triggered...)

[commit-bot: I haz the power, 2014-05-22 06:47:52]

Change committed as 272124