* 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
v8::Isolate* isolate,
      const atom::api::DesktopCapturer::Source& source) {
    mate::Dictionary dict(isolate, v8::Object::New(isolate));
    content::DesktopMediaID id = source.media_list_source.id;
    dict.Set("name", base::UTF16ToUTF8(source.media_list_source.name));
    dict.Set("id", id.ToString());
    dict.Set("thumbnail",
             atom::api::NativeImage::Create(
                 isolate, gfx::Image(source.media_list_source.thumbnail)));
    dict.Set("display_id", source.display_id);
    return ConvertToV8(isolate, dict);
  }
};
}  
namespace {
void EmitFinished(