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### Issue Details

* **Electron Version:**
  10.1.1
* **Operating System:**
  Ubuntu 20.04 + Linux 5.4.0-47-generic
* **Last Known Working Electron version:**
 7.1.2

### Expected Behavior
`webContents.getPrinters()` returns one printer. Besides, the OS provides additional virtual devices.
`webContents.print()` should open the print dialog and show those devices for selection.

### Actual Behavior
`webContents.print()` fails silently; in the print callback, `failureReason` is 'No valid printers available'

### To Reproduce
Just run `webContents.print()`

Electron fiddle: https://gist.github.com/35c5067af8ec104f86bd0cdd4a95b1f5

### Screenshots
![electron-issue](https://user-images.githubusercontent.com/5503002/93387857-3fc9b300-f840-11ea-9335-bf32a3ddea08.png)
![electron-issue](https://user-images.githubusercontent.com/5503002/93387860-40fae000-f840-11ea-938e-09c62f06f06b.gif)


### Additional Information
Upgrading an app built on Electron 7.1.2 that had printing working before

shell/browser/api/electron_api_web_contents.cc
v8::Local<v8::Value> val,
                     content::SavePageType* out) {
    std::string save_type;
    if (!ConvertFromV8(isolate, val, &save_type))
      return false;
    save_type = base::ToLowerASCII(save_type);
    if (save_type == "htmlonly") {
      *out = content::SAVE_PAGE_TYPE_AS_ONLY_HTML;
    } else if (save_type == "htmlcomplete") {
      *out = content::SAVE_PAGE_TYPE_AS_COMPLETE_HTML;
    } else if (save_type == "mhtml") {
      *out = content::SAVE_PAGE_TYPE_AS_MHTML;
    } else {
      return false;
    }
    return true;
  }
};
template <>
struct Converter<electron::api::WebContents::Type> {
  static v8::Local<v8::Value> ToV8(v8::Isolate* isolate,