linux: Don't lower windows on middle-click on KDE 4.

linux: Don't lower windows on middle-click on KDE 4.

KDE releases since 4.4 have had activated a "tab-grouping"
feature when users middle-click on window titlebars. Make
Chrome be slightly less jarring by doing nothing in response
to middle-clicks on KDE4 instead of lowering windows.

BUG=36586
Committed: https://crrev.com/fac2f8755bf16a91f6e038ca87d17d777b24b9d4
Cr-Commit-Position: refs/heads/master@{#293870}

[Daniel Erat, 2014-09-08 22:03:39]

derat@chromium.org changed reviewers:
+ erg@chromium.org, thestig@chromium.org

[Elliot Glaysher, 2014-09-08 22:04:41]

lgtm

(Year of the Linux Desktop.)

[Lei Zhang, 2014-09-08 22:33:54]

lgtm++ (verified locally)

[Daniel Erat, 2014-09-08 22:34:24]

The CQ bit was checked by derat@chromium.org

[commit-bot: I haz the power, 2014-09-08 22:37:07]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/derat@chromium.org/557503002/20001

[commit-bot: I haz the power, 2014-09-09 05:48:05]

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

[commit-bot: I haz the power, 2014-09-09 05:48:05]

Exceeded time limit waiting for builds to trigger.

[Lei Zhang, 2014-09-09 05:53:00]

The CQ bit was checked by thestig@chromium.org

[commit-bot: I haz the power, 2014-09-09 05:53:33]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/derat@chromium.org/557503002/20001

[commit-bot: I haz the power, 2014-09-09 06:23:44]

Committed patchset #2 (id:20001) as bee3f76234a44115f16f4e4409146843243efa2e

[commit-bot: I haz the power, 2014-09-10 03:51:09]

Patchset 2 (id:??) landed as
https://crrev.com/fac2f8755bf16a91f6e038ca87d17d777b24b9d4
Cr-Commit-Position: refs/heads/master@{#293870}