Set Attr.ownerDocument in Element#setAttributeNode()

Attr objects can move across documents by setAttributeNode().
So It needs to reset ownerDocument through TreeScopeAdoptr::adoptIfNeeded().

BUG=248950
TEST=set-attribute-node-from-iframe.html

Review URL: https://chromiumcodereview.appspot.com/17583003

git-svn-id: svn://svn.chromium.org/blink/trunk@152938 bbb929c8-8fbe-4397-9dbb-9b2b20218538
size_t ElementData::getAttrIndex(Attr* attr) const
{
    for (unsigned i = 0; i < length(); ++i) {
        if (attributeItem(i)->name() == attr->qualifiedName())
            return i;
    }
    return notFound;
}

size_t ElementData::getAttrIndex(Attr* attr) const
{
    for (unsigned i = 0; i < length(); ++i) {
        if (attributeItem(i)->name() == attr->qualifiedName())
            return i;
    }
    return notFound;
}
