Don't assume gfx::Screen::GetNumDisplays() == GetAllDisplays().size().

Don't assume gfx::Screen::GetNumDisplays() == GetAllDisplays().size().

It is safer to use the C++11 foreach operator to iterate over this
vector. On Windows gfx::ScreenWin gets the the display count from a
different place from the display list.

BUG=427931
Committed: https://crrev.com/dbd94f7916ed11a14deddaa53db6f84ce5fd1b57
Cr-Commit-Position: refs/heads/master@{#302416}

[Reilly Grant (use Gerrit), 2014-10-31 21:43:45]

reillyg@chromium.org changed reviewers:
+ hongbo.min@intel.com

[Reilly Grant (use Gerrit), 2014-10-31 21:49:21]

hongbo.min@intel.com, please take a look.

[Hongbo Min, 2014-11-03 01:00:28]

lgtm. thanks.

[Reilly Grant (use Gerrit), 2014-11-03 05:59:42]

The CQ bit was checked by reillyg@chromium.org

[commit-bot: I haz the power, 2014-11-03 06:00:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/689223002/1

[commit-bot: I haz the power, 2014-11-03 06:40:34]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-11-03 06:41:18]

Patchset 1 (id:??) landed as
https://crrev.com/dbd94f7916ed11a14deddaa53db6f84ce5fd1b57
Cr-Commit-Position: refs/heads/master@{#302416}