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}
Document::~Document()
{
    DCHECK(!layoutView());
    DCHECK(!parentTreeScope());
    DCHECK(!m_axObjectCache);
    InstanceCounters::decrementCounter(InstanceCounters::DocumentCounter);
}

Document::~Document()
{
    DCHECK(!layoutView());
    DCHECK(!parentTreeScope());
    DCHECK(!m_axObjectCache);
    InstanceCounters::decrementCounter(InstanceCounters::DocumentCounter);
}
