<!--  As an open source project with a dedicated but small maintainer team, it can sometimes take a long time for issues to be addressed so please be patient and we will get back to you as soon as we can.
-->

### 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:**
  * 7.0.0
* **Operating System:**
  * Windows 10 (1803)
* **Last Known Working Electron version:**
  * 6.1.2

### Expected Behavior
Loading flash content through an swf file results in the correct visualization of said content

### Actual Behavior
An error "GET http://interactive-mirror3.nfb.ca/FrameLoader.swf net::ERR_INVALID_ARGUMENT" appears:

![Annotazione 2019-10-25 170420](https://user-images.githubusercontent.com/6009920/67582177-8a829e00-f749-11e9-8e0d-1d08c4930084.png)


### To Reproduce
Try embedding this flash website in an electron project (http://bear71.nfb.ca/#/bear71) following this tutorial: https://electronjs.org/docs/tutorial/using-pepper-flash-plugin

<!--
For bugs that can be encapsulated in a small experiment, you can use Electron Fiddle (https://github.com/electron/fiddle) to publish your example to a GitHub Gist and link it your bug report.
-->

<!--
If Fiddle is insufficient to produce an example, please provide an example REPOSITORY that can be cloned and run. You can fork electron-quick-start (https://github.com/electron/electron-quick-start) and include a link to the branch with your changes.
-->

<!--
If you provide a URL, please list the commands required to clone/setup/run your repo e.g.
```sh
$ git clone $YOUR_URL -b $BRANCH
$ npm install
$ npm start || electron .
```
-->

### Screenshots
![Annotazione 2019-10-25 170420](https://user-images.githubusercontent.com/6009920/67582177-8a829e00-f749-11e9-8e0d-1d08c4930084.png)

### Additional Information
<!-- Add any other context about the problem here. -->

shell/browser/net/system_network_context_manager.cc
PrefService* pref_service) {
  DCHECK(!g_system_network_context_manager);
  g_system_network_context_manager =
      new SystemNetworkContextManager(pref_service);
  return g_system_network_context_manager;
}
SystemNetworkContextManager* SystemNetworkContextManager::GetInstance() {
  return g_system_network_context_manager;
}
void SystemNetworkContextManager::DeleteInstance() {
  DCHECK(g_system_network_context_manager);
  delete g_system_network_context_manager;
}
SystemNetworkContextManager::SystemNetworkContextManager(
    PrefService* pref_service)
    : proxy_config_monitor_(pref_service) {
  shared_url_loader_factory_ = new URLLoaderFactoryForSystem(this);
}
SystemNetworkContextManager::~SystemNetworkContextManager() {