Refine the UseCounters for DOMFocusIn/Out and focusin/out events

Refine the UseCounters for DOMFocusIn/Out and focusin/out events

Hixie asked in bug 378163:
"Should we drop focusin/focusout?"
"Is there a compat need to support the focusin/focusout events?"

To answer that question, add a UseCounter for focusin/focusout.
Instead of counting all listeners, count cases where the event is
actually fired with a listener attached, which is a better estimate of
the compatibility risk. Make the same change to the DOMFocusInOut
counter to make the two comparable.

BUG=378163
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175014

[philipj_slow, 2014-05-28 12:13:43]

tkent, you added the DOMFocusInOut counter, can you PTAL?

[philipj_slow, 2014-05-28 21:48:35]

Wait, PS1 won't work, because hasEventListeners will only catch event listeners
attached to the same node, which isn't enough for bubbling events and capturing
event handlers.

[philipj_slow, 2014-05-28 23:01:39]

There, I think PS2 ought to do it. EventTarget.cpp looks ready for a helper
function for the counting, but I didn't want to mix that into this CL.

[tkent, 2014-05-28 23:04:14]

lgtm

[commit-bot: I haz the power, 2014-05-28 23:04:43]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/philipj@opera.com/307613002/20001

[commit-bot: I haz the power, 2014-05-29 00:20:36]

Change committed as 175014