After https://bugs.webkit.org/show_bug.cgi?id=107138, RenderFlowThread should not be constructed as a renderer for Document. Since it does not have an element associated, it will be constructed using the pattern for anonymous blocks.
Created attachment 195892 [details] Patch
Created attachment 196087 [details] Patch for landing
Comment on attachment 196087 [details] Patch for landing Clearing flags on attachment: 196087 Committed r147414: <http://trac.webkit.org/changeset/147414>
All reviewed patches have been landed. Closing bug.
Comment on attachment 196087 [details] Patch for landing View in context: https://bugs.webkit.org/attachment.cgi?id=196087&action=review > Source/WebCore/rendering/RenderMultiColumnFlowThread.cpp:45 > + ASSERT(document->cssRegionsEnabled()); You should remove this line. Ultimately multicolumn layout will be on even if the CSS Regions feature is not.