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}
    explicit ParseQualifiedNameResult(QualifiedNameStatus status) : status(status) { }

    explicit ParseQualifiedNameResult(QualifiedNameStatus status) : status(status) { }
