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### Issue Details

* **Electron Version:**
  * Tested with 8.0.0 and v9.0.0-beta.1
* **Operating System:**
  * macOS 10.15.3 (19D76)
* **Last Known Working Electron version:**
  * 7.1.12

### Expected Behavior

`navigator.mediaDevices.enumerateDevices()` should return a list of MediaDevices with a `label` and a `deviceId` property. The `deviceId` property should stay the same across reloads and restarts.

### Actual Behavior
The `deviceId` property changes with every reload/restart.

### To Reproduce
Simply execute `navigator.mediaDevices.enumerateDevices()` in the renderer process and compare the ids of the media devices to a different execution.

See this fork for an example:
https://github.com/codedrift/electron-quick-start

```sh
$ git clone https://github.com/codedrift/electron-quick-start -b media-device-ids
$ npm install
$ npm start || electron .
```

### Additional Information
It seems to work fine in a regular Chrome 80 browser. 

shell/browser/electron_browser_client.cc
content::RenderFrameHost* rfh,
    content::SiteInstance* pending_site_instance) {
  
  ConsiderSiteInstanceForAffinity(rfh, pending_site_instance);
  
  auto* web_contents = content::WebContents::FromRenderFrameHost(rfh);
  auto* pending_process = pending_site_instance->GetProcess();
  pending_processes_[pending_process->GetID()] = web_contents;
  if (rfh->GetParent())
    renderer_is_subframe_.insert(pending_process->GetID());
  else
    renderer_is_subframe_.erase(pending_process->GetID());
}
void ElectronBrowserClient::AppendExtraCommandLineSwitches(
    base::CommandLine* command_line,
    int process_id) {
  
  {
    base::ThreadRestrictions::ScopedAllowIO allow_io;
    base::FilePath child_path;
    base::FilePath program =
        base::MakeAbsoluteFilePath(command_line->GetProgram());
#if defined(OS_MACOSX)
    auto renderer_child_path = content::ChildProcessHost::GetChildPath(
        content::ChildProcessHost::CHILD_RENDERER);
    auto gpu_child_path = content::ChildProcessHost::GetChildPath(
        content::ChildProcessHost::CHILD_GPU);
    auto plugin_child_path = content::ChildProcessHost::GetChildPath(
        content::ChildProcessHost::CHILD_PLUGIN);
    if (program != renderer_child_path && program != gpu_child_path &&