* Electron Version: 3.0.0-beta.2
* Operating System (Platform and Version): Current Windows 10, 64bit
* Last known working Electron version: 2.0.4

**Expected Behavior**
Full screen and all opened windows to be returned.

**Actual behavior**
Only full screen and a seemingly identical item are returned. Independent of the number of opened windows. 

**To Reproduce**
Call
```
desktopCapturer.getSources({
    types: ['window', 'screen'],
    thumbnailSize: {
          width: 250,
          height: 250
    }
}, function (err, sources) {

});
```
The `sources` contains only two items, the first one, which is the entire desktop screen is valid, the other one is not.


atom/browser/api/atom_api_desktop_capturer.cc
const auto media_list_sources = cap->media_list_->GetSources();
  std::vector<atom::api::DesktopCapturer::Source> sources;
  for (const auto& media_list_source : media_list_sources) {
    sources.emplace_back(
        atom::api::DesktopCapturer::Source{media_list_source, std::string()});
  }
#if defined(OS_WIN)
  
  
  
  
  if (cap->using_directx_capturer_) {
    std::vector<std::string> device_names;
    
    
    webrtc::DxgiDuplicatorController::Instance()->GetDeviceNames(&device_names);
    int device_name_index = 0;
    for (auto& source : sources) {
      if (source.media_list_source.id.type ==
          content::DesktopMediaID::TYPE_SCREEN) {