### 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.
* [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
return;
  }
  if (current_request_uses_header_client_ && !redirect_url_.is_empty()) {
    HandleBeforeRequestRedirect();
    return;
  }
  if (proxied_client_binding_.is_bound())
    proxied_client_binding_.ResumeIncomingMethodCallProcessing();
  if (header_client_receiver_.is_bound())
    header_client_receiver_.Resume();
  if (!target_loader_.is_bound() && factory_->target_factory_.is_bound()) {
    
    
    network::mojom::URLLoaderClientPtr proxied_client;
    proxied_client_binding_.Bind(mojo::MakeRequest(&proxied_client));
    uint32_t options = options_;
    
    
    if (has_any_extra_headers_listeners_)
      options |= network::mojom::kURLLoadOptionUseHeaderClient;
    factory_->target_factory_->CreateLoaderAndStart(
        mojo::MakeRequest(&target_loader_), routing_id_,
        network_service_request_id_, options, request_,
        std::move(proxied_client), traffic_annotation_);
  }
  
  
  
}
void ProxyingURLLoaderFactory::InProgressRequest::