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}
static bool shouldInheritSecurityOriginFromOwner(const KURL& url)
{
    return url.isEmpty() || url.protocolIsAbout();
}

static bool shouldInheritSecurityOriginFromOwner(const KURL& url)
{
    return url.isEmpty() || url.protocolIsAbout();
}
