Merge three implementations for getting the topmost x11 window at a point

Introduce X11TopmostWindowFinder which merges the mostly duplicated functionality to find the topmost window at a point in:
- window_finder_x11.cc
- desktop_drag_drop_client_aurax11.cc
- desktop_screen_x11.cc

Having all of the similar functionality in one place will be helpful for testing

BUG=None
TEST=None

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=268001

[pkotwicz, 2014-04-29 02:27:46]

Sadrul, PTAL

I am planning on adding tests for this class in my next CL. (It is as good of a
candidate as any)
- Unit tests will be useful once we add a cache that can be queried for the
toplevel window (In particular, there are certain non-obvious optimizations
which can be done. (e.g. it is possible to figure out whether a window is
minimized by querying the shape extension)
- I think that the non-EWMH implementation is wrong

https://codereview.chromium.org/260263002/diff/30001/ui/views/widget/desktop_...
File ui/views/widget/desktop_aura/x11_topmost_window_finder.cc (right):

https://codereview.chromium.org/260263002/diff/30001/ui/views/widget/desktop_...
ui/views/widget/desktop_aura/x11_topmost_window_finder.cc:75:
window->GetBoundsInScreen().Contains(screen_loc_);
For an upcoming CL:
Checking the bounds is wrong. aura::Window::HitTest() is probably more accurate.
However, that still misses the rounded corners when the window is restored.

[sadrul, 2014-04-30 19:38:41]

+erg@

[Elliot Glaysher, 2014-04-30 19:45:55]

This is something I've wanted done for a long time. Thank you for doing this.
lgtm.

[pkotwicz, 2014-04-30 20:36:19]

Scott can you please take a look at the change in chrome/browser/ui/views/tabs

[sky, 2014-04-30 21:21:12]

Nice, LGTM

[pkotwicz, 2014-05-02 21:22:42]

The CQ bit was checked by pkotwicz@chromium.org

[commit-bot: I haz the power, 2014-05-02 21:23:51]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/pkotwicz@chromium.org/260263002/30001

[commit-bot: I haz the power, 2014-05-03 02:07:49]

Change committed as 268001