Always use FrameNavigationDisabler during DocumentLoader detach.

BUG=617495

Review-Url: https://codereview.chromium.org/2079473002
Cr-Commit-Position: refs/heads/master@{#400558}
bool FrameLoader::allowPlugins(ReasonForCallingAllowPlugins reason)
{
    if (!client())
        return false;
    Settings* settings = m_frame->settings();
    bool allowed = client()->allowPlugins(settings && settings->pluginsEnabled());
    if (!allowed && reason == AboutToInstantiatePlugin)
        client()->didNotAllowPlugins();
    return allowed;
}

bool FrameLoader::allowPlugins(ReasonForCallingAllowPlugins reason)
{
    if (!client())
        return false;
    Settings* settings = m_frame->settings();
    bool allowed = client()->allowPlugins(settings && settings->pluginsEnabled());
    if (!allowed && reason == AboutToInstantiatePlugin)
        client()->didNotAllowPlugins();
    return allowed;
}
