Attempt to address libxml crash.

BUG=129930
Review URL: https://chromiumcodereview.appspot.com/10458051

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@142822 0039d316-1c4b-4281-b951-d872f2087c98
xmlThrDefOutputBufferCreateFilenameDefault(xmlOutputBufferCreateFilenameFunc func)
{
    xmlOutputBufferCreateFilenameFunc old;
    
    xmlMutexLock(xmlThrDefMutex);
    old = xmlOutputBufferCreateFilenameValueThrDef;
#ifdef LIBXML_OUTPUT_ENABLED
    if (old == NULL) {
		old = __xmlOutputBufferCreateFilename;
	}
#endif
    xmlOutputBufferCreateFilenameValueThrDef = func;
    xmlMutexUnlock(xmlThrDefMutex);

    return(old);
}

xmlThrDefOutputBufferCreateFilenameDefault(xmlOutputBufferCreateFilenameFunc func)
{
    xmlOutputBufferCreateFilenameFunc old;
    
    xmlMutexLock(xmlThrDefMutex);
    old = xmlOutputBufferCreateFilenameValueThrDef;
#ifdef LIBXML_OUTPUT_ENABLED
    if (old == NULL) {
		old = __xmlOutputBufferCreateFilename;
	}
#endif
    xmlOutputBufferCreateFilenameValueThrDef = func;
    xmlMutexUnlock(xmlThrDefMutex);

    return(old);
}
