Mouseup event does not fire on Scroll Bar
https://bugs.webkit.org/show_bug.cgi?id=25811

Reviewed by Tony Chang.

Source/WebCore:

Currently, clicking on a scrollbar fires a mousedown event, but not a
mouseup event. This causes problems for code like jQuery UI's
draggable[1], as the drag starts, but is never cancelled. Other use
cases are noted in the slightly old Chromium bug[2].

If a mouseup event is received after a mousedown event on a scrollbar,
this patch dispatches a mouseup event on the same node the mousedown
event dispatched on. This matches Gecko's behavior.

[1]: http://bugs.jqueryui.com/ticket/6925
[2]: http://crbug.com/14204

Tests: fast/scrolling/scrollbar-mousedown-mouseup.html
       fast/scrolling/scrollbar-mousedown-move-mouseup.html

* page/EventHandler.cpp:
(WebCore::EventHandler::handleMouseReleaseEvent):
    If a mouseup event follow a mousedown event on a scrollbar,
    dispatch an event on the same node from which the mousedown event
    was triggered.

LayoutTests:

* fast/scrolling/scrollbar-mousedown-mouseup-expected.txt: Added.
* fast/scrolling/scrollbar-mousedown-mouseup.html: Added.
* fast/scrolling/scrollbar-mousedown-move-mouseup-expected.txt: Added.
* fast/scrolling/scrollbar-mousedown-move-mouseup.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143560 268f45cc-cd09-0410-ab3c-d52691b4dbfc