Remove WebFrame::canHaveSecureChild

To simplify the public API, ServiceWorkerNetworkProvider can do the
parent walk itself.

Follow-up to https://crrev.com/ad1850962644e19.

BUG=607543

Review-Url: https://codereview.chromium.org/2082493002
Cr-Commit-Position: refs/heads/master@{#400896}
 Frame::Frame(FrameClient* client, FrameHost* host, FrameOwner* owner)
     : m_treeNode(this)
     , m_host(host)
    , m_owner(owner)
    , m_client(client)
    , m_isLoading(false)
{
    InstanceCounters::incrementCounter(InstanceCounters::FrameCounter);

    ASSERT(page());

    if (m_owner)
        m_owner->setContentFrame(*this);
    else
        page()->setMainFrame(this);
}

 Frame::Frame(FrameClient* client, FrameHost* host, FrameOwner* owner)
     : m_treeNode(this)
     , m_host(host)
    , m_owner(owner)
    , m_client(client)
    , m_isLoading(false)
{
    InstanceCounters::incrementCounter(InstanceCounters::FrameCounter);

    ASSERT(page());

    if (m_owner)
        m_owner->setContentFrame(*this);
    else
        page()->setMainFrame(this);
}
