RenderScrollbar: Map of scrollbar parts should use RenderPtr.
<https://webkit.org/b/126367>

Turn RenderScrollbar::m_parts into HashMap of RenderPtrs. This makes
renderer destruction automatic and lets us remove some code.

Reviewed by Antti Koivisto.

* rendering/RenderPtr.h:

    Add HashTraits for RenderPtr so we can use them as values in
    WTF hash tables.

* rendering/RenderScrollbar.h:
* rendering/RenderScrollbar.cpp:
(WebCore::RenderScrollbar::~RenderScrollbar):
(WebCore::RenderScrollbar::setParent):
(WebCore::RenderScrollbar::updateScrollbarParts):
(WebCore::RenderScrollbar::updateScrollbarPart):

    Remove now-unneeded kludges of logic to manually delete scrollbar
    part renderers in various scenarios.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@161200 268f45cc-cd09-0410-ab3c-d52691b4dbfc
[EFL] Unreviewed build fix after r160903 when ACCESSIBILITY is disabled

* accessibility/AccessibilityObject.h:
(WebCore::AccessibilityObject::children):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@161201 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Fix the build by exposing some more scrolling state node headers
as Private in WebCore.framework.

* WebCore.xcodeproj/project.pbxproj:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@161202 268f45cc-cd09-0410-ab3c-d52691b4dbfc