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### 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
This is a bug report specifically for the 7.0 beta. 

* **Electron Version:**
  * 7.0.0-beta.6
* **Operating System:**
  * Ubuntu 18.04 x64, Windows 10
* **Last Known Working Electron version:**
  * 6.0.12

### Expected Behavior
SharedWorker should be functional and *shared* when using
  a custom protocol to provide a proper origin.

### Actual Behavior
SharedWorker does not execute when loaded from custom protocol.
It does execute when page is loaded with the `file://` protocol, but this 
  defeats the purpose, since it is not shared between contexts.

Also noticed while diagnosing the issue:
Creating a SharedWorker with node integration enabled using a Data URL crashes 
the renderer.  I verified that this works in Electron 6, figured the cause might be related.

### To Reproduce
Install and run the following repo:

https://github.com/krisdages/electron-7-shared-worker-broken

$ git clone https://github.com/krisdages/electron-7-shared-worker-broken
$ npm install
$ npm start

Sorry, had it implemented before seeing the "electron fiddle" option. May try that next time.

Thanks for looking into this :)
shell/browser/electron_browser_client.cc
#endif
    if (delegate_) {
      auto app_path = static_cast<api::App*>(delegate_)->GetAppPath();
      command_line->AppendSwitchPath(switches::kAppPath, app_path);
    }
    std::unique_ptr<base::Environment> env(base::Environment::Create());
    if (env->HasVar("ELECTRON_PROFILE_INIT_SCRIPTS")) {
      command_line->AppendSwitch("profile-electron-init");
    }
    content::WebContents* web_contents =
        GetWebContentsFromProcessID(process_id);
    if (web_contents) {
      auto* web_preferences = WebContentsPreferences::From(web_contents);
      if (web_preferences)
        web_preferences->AppendCommandLineSwitches(
            command_line, IsRendererSubFrame(process_id));
      auto preloads = SessionPreferences::GetValidPreloads(
          web_contents->GetBrowserContext());
      if (!preloads.empty())
        command_line->AppendSwitchNative(
            switches::kPreloadScripts,
            base::JoinString(preloads, kPathDelimiter));
      if (CanUseCustomSiteInstance()) {
        command_line->AppendSwitch(
            switches::kDisableElectronSiteInstanceOverrides);
      }
    }
  }
}
void ElectronBrowserClient::DidCreatePpapiPlugin(