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}
PassRefPtrWillBeRawPtr<Range> Document::createRange()
{
    return Range::create(*this);
}

PassRefPtrWillBeRawPtr<Range> Document::createRange()
{
    return Range::create(*this);
}
