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}
    ParseQualifiedNameResult(QualifiedNameStatus status, UChar32 character) : status(status), character(character) { }

    ParseQualifiedNameResult(QualifiedNameStatus status, UChar32 character) : status(status), character(character) { }
