### Preflight Checklist

* [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:**
  * v8.0.0-nightly.20190821
* **Operating System:**
  * Ubuntu 19.04 x64
* **Last Known Working Electron version:**
  * Unknown. Broken in `4-1-x` upwards.

### Expected Behavior

Passing additional schemes on the command line, e.g. `--standard-schemes=foo,bar,mum`, should not affect other schemes, e.g. cors enabled schemes or secure schemes.

### Actual Behavior

The schemes from earlier checks bleed into all the following switches checked.

This happens due to the "splitted" variable in `shell/app/atom_content_client.cc`'s `AtomContentClient::AddAdditionalSchemes()` being reused for each switch without being cleared first.

### To Reproduce

On the command line, add schemes for one of the argument switches handled in `AtomContentClient::AddAdditionalSchemes()`.

shell/app/atom_content_client.cc
int resource_id) {
  return ui::ResourceBundle::GetSharedInstance().LoadDataResourceBytes(
      resource_id);
}
void AtomContentClient::AddAdditionalSchemes(Schemes* schemes) {
  std::vector<std::string> splited;
  ConvertStringWithSeparatorToVector(&splited, ",",
                                     switches::kServiceWorkerSchemes);
  for (const std::string& scheme : splited)
    schemes->service_worker_schemes.push_back(scheme);
  schemes->service_worker_schemes.push_back(url::kFileScheme);
  ConvertStringWithSeparatorToVector(&splited, ",", switches::kStandardSchemes);
  for (const std::string& scheme : splited)
    schemes->standard_schemes.push_back(scheme);
  schemes->standard_schemes.push_back("chrome-extension");
  ConvertStringWithSeparatorToVector(&splited, ",", switches::kSecureSchemes);
  for (const std::string& scheme : splited)
    schemes->secure_schemes.push_back(scheme);
  ConvertStringWithSeparatorToVector(&splited, ",",
                                     switches::kBypassCSPSchemes);
  for (const std::string& scheme : splited)
    schemes->csp_bypassing_schemes.push_back(scheme);
  ConvertStringWithSeparatorToVector(&splited, ",", switches::kCORSSchemes);
  for (const std::string& scheme : splited)
    schemes->cors_enabled_schemes.push_back(scheme);
}
void AtomContentClient::AddPepperPlugins(