Revert: [Refactor] Consolidate the logic for whether a widget can be activated. This is a first ste

Revert of [Refactor] Consolidate the logic for whether a widget can be activated. (https://codereview.chromium.org/286733002/)

Reason for revert:
This CL was causing problems when the value of views::Widget::CanActivate() changes crbug.com/374095 

I also need to audit the code to find out whether there are any 'non-activatable' widgets which were intended to be activatable

Original issue's description:
> [Refactor] Consolidate the logic for whether a widget can be activated.
> 
> This is a first step towards giving tooltips their own WindowTreeHosts on Linux.
> 
> BUG=353533
> TEST=None
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=270597

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=271468

[pkotwicz, 2014-05-19 20:40:39]

Committed patchset #1 manually as r271468.