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
xmlThrDefDeregisterNodeDefault(xmlDeregisterNodeFunc func)
{
    xmlDeregisterNodeFunc old;

    xmlMutexLock(xmlThrDefMutex);
    old = xmlDeregisterNodeDefaultValueThrDef;
    
    __xmlRegisterCallbacks = 1;
    xmlDeregisterNodeDefaultValueThrDef = func;
    xmlMutexUnlock(xmlThrDefMutex);

    return(old);
}

xmlThrDefDeregisterNodeDefault(xmlDeregisterNodeFunc func)
{
    xmlDeregisterNodeFunc old;

    xmlMutexLock(xmlThrDefMutex);
    old = xmlDeregisterNodeDefaultValueThrDef;
    
    __xmlRegisterCallbacks = 1;
    xmlDeregisterNodeDefaultValueThrDef = func;
    xmlMutexUnlock(xmlThrDefMutex);

    return(old);
}
