### Preflight Checklist
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* [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.
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### 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
proxied_loader_binding_(this, std::move(loader_request)),
      target_client_(std::move(client)),
      current_response_(network::mojom::URLResponseHead::New()),
      proxied_client_binding_(this),
      
      
      
      has_any_extra_headers_listeners_(network_service_request_id != 0) {
  
  target_client_.set_connection_error_handler(base::BindOnce(
      &ProxyingURLLoaderFactory::InProgressRequest::OnRequestError,
      weak_factory_.GetWeakPtr(),
      network::URLLoaderCompletionStatus(net::ERR_ABORTED)));
}
ProxyingURLLoaderFactory::InProgressRequest::~InProgressRequest() {
  
  
  if (info_) {
    factory_->web_request_api()->OnRequestWillBeDestroyed(&info_.value());
  }
  if (on_before_send_headers_callback_) {
    std::move(on_before_send_headers_callback_)
        .Run(net::ERR_ABORTED, base::nullopt);
  }
  if (on_headers_received_callback_) {
    std::move(on_headers_received_callback_)
        .Run(net::ERR_ABORTED, base::nullopt, base::nullopt);
  }
}
void ProxyingURLLoaderFactory::InProgressRequest::Restart() {