### 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
HandleBeforeRequestRedirect() {
  
  
  
  
  
  
  
  
  proxied_client_binding_.Close();
  header_client_receiver_.reset();
  target_loader_.reset();
  constexpr int kInternalRedirectStatusCode = 307;
  net::RedirectInfo redirect_info;
  redirect_info.status_code = kInternalRedirectStatusCode;
  redirect_info.new_method = request_.method;
  redirect_info.new_url = redirect_url_;
  redirect_info.new_site_for_cookies = redirect_url_;
  auto head = network::mojom::URLResponseHead::New();
  std::string headers = base::StringPrintf(
      "HTTP/1.1 %i Internal Redirect\n"
      "Location: %s\n"
      "Non-Authoritative-Reason: WebRequest API\n\n",
      kInternalRedirectStatusCode, redirect_url_.spec().c_str());
  if (factory_->browser_context_->ShouldEnableOutOfBlinkCors()) {