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* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

* **Electron Version:** 
  * v7.0.0-beta.6
* **Operating System:** 
  * macOS Mojave 10.14.5
* **Last Known Working Electron version:** 
  * v6.0.12

### Expected Behavior
<!-- A clear and concise description of what you expected to happen. -->

The electron helper process should not eat up memory.

<img width="815" alt="Screenshot 2019-10-10 at 11 29 35" src="https://user-images.githubusercontent.com/1265681/66556996-7b98ca80-eb51-11e9-894f-7f6323deab7f.png">


### Actual Behavior
<!-- A clear and concise description of what actually happened. -->

An electron helper process eats up memory in a linear way

<img width="898" alt="Screenshot 2019-10-10 at 11 23 35" src="https://user-images.githubusercontent.com/1265681/66557157-b438a400-eb51-11e9-954a-56cc236c72c6.png">


![Electron Helper_48309 (1)](https://user-images.githubusercontent.com/1265681/66557054-93704e80-eb51-11e9-8507-ba76bafaa03e.png)



### To Reproduce
<!--
Your best chance of getting this bug looked at quickly is to provide an example.
-->

<!--
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.
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#### Example Repositiory

Here is a minimal reproduction example: https://github.com/HaNdTriX/electron-memory-leak

<!--
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.
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```sh
$ git clone git@github.com:HaNdTriX/electron-memory-leak.git
$ cd electron-memory-leak
$ npm install
$ npm start
```

After starting the app please take a look at its memory usage.

#### Code

```js
const { session, app, protocol, BrowserWindow } = require('electron')
const { join } = require('path')

protocol.registerSchemesAsPrivileged([{
  scheme: 'atom',
  privileges: {
    // The following setting
    // is causing the memoryleak
    standard: true
  }
}])

app.on('ready', () => {
  session.defaultSession.protocol.registerFileProtocol('atom', (request, callback) => {
    callback({
      path: join(__dirname, 'index.html')
    })
  })

  mainWindow = new BrowserWindow({
    width: 800,
    height: 600
  })

  mainWindow.loadURL(`atom://foobar`)
})
```

### Screenshots

See above...

### Additional Information

I've tracked down the bug to `registerSchemesAsPrivileged` and its `standard` setting. 

shell/browser/atom_browser_client.cc
const GURL& url,
    content::WebContents::Getter web_contents_getter,
    int child_id,
    content::NavigationUIData* navigation_data,
    bool is_main_frame,
    ui::PageTransition page_transition,
    bool has_user_gesture,
    network::mojom::URLLoaderFactoryPtr* out_factory) {
  base::PostTask(FROM_HERE, {BrowserThread::UI},
                 base::BindOnce(&HandleExternalProtocolInUI, url,
                                web_contents_getter, has_user_gesture));
  return true;
}
std::vector<std::unique_ptr<content::NavigationThrottle>>
AtomBrowserClient::CreateThrottlesForNavigation(
    content::NavigationHandle* handle) {
  std::vector<std::unique_ptr<content::NavigationThrottle>> throttles;
  throttles.push_back(std::make_unique<AtomNavigationThrottle>(handle));
  return throttles;
}
content::MediaObserver* AtomBrowserClient::GetMediaObserver() {