Reviewed by Antti Koivisto.

Page::m_dragCaretController is never null.

* dom/Document.cpp:
(WebCore::Document::nodeChildrenWillBeRemoved):
(WebCore::Document::nodeWillBeRemoved):
* page/DragController.cpp:
(WebCore::DragController::cancelDrag):
(WebCore::DragController::dragEnded):
(WebCore::DragController::tryDocumentDrag):
(WebCore::DragController::dispatchTextInputEventFor):
(WebCore::DragController::concludeEditDrag):
(WebCore::DragController::placeDragCaret):
* page/Page.h:
(WebCore::Page::dragCaretController):
* rendering/RenderBlock.cpp:
(WebCore::RenderBlock::paintCaret):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154238 268f45cc-cd09-0410-ab3c-d52691b4dbfc