Rename is_chromeos in libjingle.

Rename is_chromeos in libjingle.

is_chromeos does a poor job of distinguishing developer builds of
chrome for chromeos for your desktop, and chrome for chromeos on
a device (where the runtimes are non local, for example)

Split this into is_chromeos_ui and is_chromeos_os.

BUG=519943
TEST=ChromiumOS compiles equivalently.

[Peter Mayo, 2015-08-13 01:24:17]

Dependent on https://codereview.chromium.org/1283313004/

upload suggested kjellander@ as a reviewer.
git-cl picks on tommi@

[tommi (sloooow) - chröme, 2015-08-13 08:36:00]

tommi@chromium.org changed reviewers:
+ tommi@chromium.org

[tommi (sloooow) - chröme, 2015-08-13 08:36:01]

lgtm. kjellander is currently ooo fyi

[tommi (sloooow) - chröme, 2015-08-14 10:18:04]

The CQ bit was checked by tommi@chromium.org

[commit-bot: I haz the power, 2015-08-14 10:18:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1290033003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1290033003/1

[commit-bot: I haz the power, 2015-08-14 10:21:09]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-14 10:21:09]

Try jobs failed on following builders:
  linux_chromium_gn_chromeos_rel on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[Peter Mayo, 2015-08-14 16:37:36]

On 2015/08/14 10:21:09, commit-bot: I haz the power wrote:
> Try jobs failed on following builders:
>   linux_chromium_gn_chromeos_rel on tryserver.chromium.linux (JOB_FAILED,
>
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

This patch is dependent on https://codereview.chromium.org/1283313004/

No CQ until that is finalized and landed.