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 Document::postInspectorTask(const WebTraceLocation& location, std::unique_ptr<ExecutionContextTask> task)
{
    m_taskRunner->postInspectorTask(location, std::move(task));
}

void Document::postInspectorTask(const WebTraceLocation& location, std::unique_ptr<ExecutionContextTask> task)
{
    m_taskRunner->postInspectorTask(location, std::move(task));
}
