[CSS Regions] Remove m_flowThread from NodeRenderingContext
https://bugs.webkit.org/show_bug.cgi?id=114732

Reviewed by Antti Koivisto.

Cleanup NodeRenderingContext. Remove unused member m_flowThread.

Tests: None needed.

* dom/NodeRenderingContext.cpp:
(WebCore::NodeRenderingContext::moveToFlowThreadIfNeeded):
* dom/NodeRenderingContext.h: Removed m_flowThread.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148605 268f45cc-cd09-0410-ab3c-d52691b4dbfc