Change MouseEventWithHitTestResults to hold onto a HitTestResult

Change MouseEventWithHitTestResults to hold onto a HitTestResult

Reviewed by Sam.

* dom/Document.cpp:
(WebCore::Document::prepareMouseEvent):
* page/MouseEventWithHitTestResults.cpp:
(WebCore::MouseEventWithHitTestResults::MouseEventWithHitTestResults):
(WebCore::MouseEventWithHitTestResults::targetNode):
(WebCore::MouseEventWithHitTestResults::localPoint):
(WebCore::MouseEventWithHitTestResults::scrollbar):
* page/MouseEventWithHitTestResults.h:
(WebCore::MouseEventWithHitTestResults::event):
(WebCore::MouseEventWithHitTestResults::hitTestResult):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@23994 268f45cc-cd09-0410-ab3c-d52691b4dbfc