ActivationTrackerWin: General refactor, renaming and clarification.

ActivationTrackerWin: General refactor, renaming and clarification.

I found this class quite difficult to understand, mostly due to bad
method and variable names. Renamed:
  CheckTaskbarOrViewHasFocus -> MaybeDismissAppList,
  RegainNextLostFocus -> ReactivateOnNextFocusLoss,
  regain_next_lost_focus_ -> reactivate_on_next_focus_loss_,
  preserving_focus_for_taskbar_menu_ -> taskbar_has_focus_,
and rewrote many of the comments for clarity.

Factored out most of the logic in MaybeDismissAppList to
ShouldDismissAppList, which returns a bool and has minimal side effects.

This also introduces a minor behavioural fix: If the focused window is
NULL, and reactivate_on_next_focus_loss is true, reactivates instead of
dismissing.

BUG=307837
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=233244

[koz (OOO until 15th September), 2013-11-06 04:19:10]

lgtm!

Awesome change, Matt! Thanks for this.

[commit-bot: I haz the power, 2013-11-06 04:39:14]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mgiuca@chromium.org/59063009/20001

[commit-bot: I haz the power, 2013-11-06 07:52:50]

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, 2013-11-06 08:23:09]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mgiuca@chromium.org/59063009/20001

[commit-bot: I haz the power, 2013-11-06 08:26:29]

Change committed as 233244