Revert of mash: Close system tray bubble on click outside its bounds, part 1

Revert of mash: Close system tray bubble on click outside its bounds, part 1 (patchset #4 id:60001 of https://codereview.chromium.org/1876553002/ )

Reason for revert:
Breaks clicking in the system tray bubble on mus. We need an entirely different architecture for this.


Original issue's description:
> mash: Close system tray bubble on click outside its bounds, part 1
> 
> Mus does not support global event handlers, so the existing TrayEventFilter
> cannot be used to close the bubble. Instead we use mouse capture.
> 
> * Capture the mouse explicitly when the bubble is spawned and release it on
> clicks outside its bounds.
> * Always close the bubble on capture loss, in case some other part of the
> window system breaks capture.
> 
> Also fix an issue with auto-release-capture at the widget level. If a view
> explicitly requested capture via Widget::SetCapture(my_view) and explicitly
> did not request auto-release-capture, then any mouse release event would
> cause the view to lose capture (that is, being an explicit mouse handler
> target at the RootView level). Fix this so that these sorts of views will
> continue to receive events until they explicit release capture.
> 
> Note that this code still eats the mousedown event that causes the bubble to
> close. Fixing that is part 2.
> 
> BUG=599142
> 
> Committed: https://crrev.com/5eb778dc5a2a4762fe95d67f2adc151f928d7939
> Cr-Commit-Position: refs/heads/master@{#386402}

TBR=sky@chromium.org,msw@chromium.org,sadrul@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=599142

[James Cook, 2016-04-14 22:52:20]

Created Revert of mash: Close system tray bubble on click outside its bounds,
part 1