Make sure pseudo-element HitTestResult::m_innerNode is not lost after a style recalc

When HitTestResult is ready, Document::prepareMouseEvent() calls updateHoverActiveState(),
which invokes style recalc, and this may remove a pseudo-element m_innerNode from its
parent element. In this case, the parent element should become the new m_innerNode.

Also, the m_innerNonSharedNode has been reverted to never hold pseudo-elements,
since this functionality is not required for DevTools.

R=esprehn, tasak
BUG=305393

Review URL: https://codereview.chromium.org/26573005

git-svn-id: svn://svn.chromium.org/blink/trunk@159658 bbb929c8-8fbe-4397-9dbb-9b2b20218538