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}
void Frame::didChangeVisibilityState()
{
    HeapVector<Member<Frame>> childFrames;
    for (Frame* child = tree().firstChild(); child; child = child->tree().nextSibling())
        childFrames.append(child);
    for (size_t i = 0; i < childFrames.size(); ++i)
         childFrames[i]->didChangeVisibilityState();
 }

void Frame::didChangeVisibilityState()
{
    HeapVector<Member<Frame>> childFrames;
    for (Frame* child = tree().firstChild(); child; child = child->tree().nextSibling())
        childFrames.append(child);
    for (size_t i = 0; i < childFrames.size(); ++i)
         childFrames[i]->didChangeVisibilityState();
 }
