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::findFrameForNavigation(const AtomicString& name, Frame& activeFrame)
{
    Frame* frame = tree().find(name);
    if (!frame || !activeFrame.canNavigate(*frame))
        return nullptr;
    return frame;
}

Frame* Frame::findFrameForNavigation(const AtomicString& name, Frame& activeFrame)
{
    Frame* frame = tree().find(name);
    if (!frame || !activeFrame.canNavigate(*frame))
        return nullptr;
    return frame;
}
