Try to reduce the flakiness of 4 :hover tests.

Try to reduce the flakiness of 4 :hover tests.
    
Based on what is currently done throughout the LayoutTests/, there
are 2 ways to reduce the flakiness of a :hover test:
* Force layout before and after moving the mouse (especially since
some tests claim that we don't track the mouse before first layout).
* Force a click after moving the mouse.

This change implements the first option as the second one didn't work
for these tests (I remember that it helped in webkit.org/b/81460
though).

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=150693

[Julien - ping for review, 2013-05-20 19:53:40]

3 try runs without any of the tests failing, it seems like it did the trick.

[eseidel, 2013-05-20 19:54:32]

lgtm

OK.

[commit-bot: I haz the power, 2013-05-20 19:54:37]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jchaffraix@chromium.org/15373002/3001

[commit-bot: I haz the power, 2013-05-20 21:09:16]

Change committed as 150693