Roll libxslt to 891681e3e948f31732229f53cb6db7215f740fc7

BUG=583156,583171

Review URL: https://codereview.chromium.org/1853083002

Cr-Commit-Position: refs/heads/master@{#385338}
xsltInitGlobals(void)
{
    if (xsltExtMutex == NULL) {
        xsltExtMutex = xmlNewMutex();
    }
}

xsltInitGlobals(void)
{
    if (xsltExtMutex == NULL) {
        xsltExtMutex = xmlNewMutex();
    }
}
