Change Document::detach() to RELEASE_ASSERT all subframes are gone.

BUG=556724,577105

Review URL: https://codereview.chromium.org/1667573002

Cr-Commit-Position: refs/heads/master@{#373642}
void Document::updateRangesAfterNodeMovedToAnotherDocument(const Node& node)
{
    ASSERT(node.document() != this);
    if (m_ranges.isEmpty())
        return;

    AttachedRangeSet ranges = m_ranges;
    for (Range* range : ranges)
        range->updateOwnerDocumentIfNeeded();
}

void Document::updateRangesAfterNodeMovedToAnotherDocument(const Node& node)
{
    ASSERT(node.document() != this);
    if (m_ranges.isEmpty())
        return;

    AttachedRangeSet ranges = m_ranges;
    for (Range* range : ranges)
        range->updateOwnerDocumentIfNeeded();
}
