start layout until <html:head> closes if <html:head> gets opened. For XHTML documents, this should prevent flashes of unstyled content. Also, don't flush tags unless forced to if a sheet is pending. Bug 380028, r+sr=sicking git-svn-id: svn://10.0.0.236/trunk@229666 18797224-902f-48f8-a5cc-f745e15eee43