### Preflight Checklist
<!-- Please ensure you've completed the following steps by replacing [ ] with [x]-->

* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

* **Electron Version:** 7.1.2
* **Operating System:** Ubuntu 18.04 x64 
* **Last Known Working Electron version:** 6.x

### Expected Behavior
Setting the "ignore-connections-limit" commandLine switch for localhost should allow more than 4 connections to e.g. the gatsby development server, which limits it to that number. This is the behaviour in Electron@6

### Actual Behavior
The "ignore-connections-limit" seems to have no effect anymore in electron@7.

### To Reproduce

1. Run a gatsby local server, like https://github.com/gatsbyjs/gatsby-starter-hello-world
2. Launch this fiddle with electron@6, and see that all 6 iframes load the site: https://gist.github.com/Kilian/d35badc28200c3229b1028243433cf54
3. Launch the fiddle with electron@7, see that none of the iframes load anymore
4. Remove two iframes, launch with electron@7, see that the iframes now do load

### Note
Note that our documentation still mentions the flag as working: https://electronjs.org/docs/api/chrome-command-line-switches#--ignore-connections-limitdomains
shell/browser/net/proxying_url_loader_factory.cc
const net::RedirectInfo& redirect_info,
    network::mojom::URLResponseHeadPtr head) {
  
  if (current_request_uses_header_client_) {
    
    
    auto saved_headers = current_response_->headers;
    current_response_ = std::move(head);
    
    
    
    if (saved_headers)
      current_response_->headers = saved_headers;
    ContinueToBeforeRedirect(redirect_info, net::OK);
  } else {
    current_response_ = std::move(head);
    HandleResponseOrRedirectHeaders(
        base::BindOnce(&InProgressRequest::ContinueToBeforeRedirect,
                       weak_factory_.GetWeakPtr(), redirect_info));
  }
}
void ProxyingURLLoaderFactory::InProgressRequest::OnUploadProgress(
    int64_t current_position,
    int64_t total_size,
    OnUploadProgressCallback callback) {
  target_client_->OnUploadProgress(current_position, total_size,
                                   std::move(callback));
}
void ProxyingURLLoaderFactory::InProgressRequest::OnReceiveCachedMetadata(