Remove obsolete OS handling in GN.

Remove obsolete OS handling in GN.

There was a a bunch of built-in special-casing of the current_os variable which has been gradually removed over time as we have needed extra flexibility and reduced special casing.

The only use of this was for libs ending in .framework on Mac. I think it's OK to run the special-casing on all OS's, since in pracice libraries on Windows and Linux can't end in ".framework".

A bunch of setup and maintenance of these variables is removed.

Committed: https://crrev.com/d4f9637d51829c0d779e7ce07b945e8b7813397d
Cr-Commit-Position: refs/heads/master@{#359170}

[brettw, 2015-11-11 00:49:13]

brettw@chromium.org changed reviewers:
+ scottmg@chromium.org

[brettw, 2015-11-11 00:49:18]

The CQ bit was checked by brettw@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-11-11 00:51:14]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1431323003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1431323003/20001

[commit-bot: I haz the power, 2015-11-11 01:11:47]

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

[commit-bot: I haz the power, 2015-11-11 01:11:48]

Dry run: This issue passed the CQ dry run.

[scottmg, 2015-11-11 04:06:50]

lgtm

Maybe in the comment/doc you could add something about it being for Mac, even
though it runs for all targets now.

[brettw, 2015-11-11 21:33:33]

The CQ bit was checked by brettw@chromium.org

[brettw, 2015-11-11 21:33:33]

The patchset sent to the CQ was uploaded after l-g-t-m from scottmg@chromium.org
Link to the patchset: https://codereview.chromium.org/1431323003/#ps40001
(title: " ")

[commit-bot: I haz the power, 2015-11-11 21:36:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1431323003/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1431323003/40001

[commit-bot: I haz the power, 2015-11-11 22:12:04]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-11-12 20:00:59]

Patchset 3 (id:??) landed as
https://crrev.com/d4f9637d51829c0d779e7ce07b945e8b7813397d
Cr-Commit-Position: refs/heads/master@{#359170}