Move event handler to window_selector to ensure correct lifetime.

Move event handler to window_selector to ensure correct lifetime.

BUG=279562
TEST=With --ash-enable-overview-mode, start alt-tabbing, click a window, then press and release alt. There should be no crash.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=221123

[flackr, 2013-09-03 15:15:24]

PTAL, this fixes a crash resulting from not cleaning up the alt key event
listener. Moving it to be scoped to the window_selector ensures the lifetime is
correct.

[Daniel Erat, 2013-09-03 15:33:22]

lgtm

[commit-bot: I haz the power, 2013-09-03 15:45:13]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/flackr@chromium.org/23529006/11007

[commit-bot: I haz the power, 2013-09-04 00:41:40]

Retried try job too often on win7_aura for step(s) browser_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win7_aura&...

[commit-bot: I haz the power, 2013-09-04 00:51:12]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/flackr@chromium.org/23529006/11007

[commit-bot: I haz the power, 2013-09-04 02:34:12]

Change committed as 221123