* Electron version: 1.7.5
* Operating system: WIndows

### Expected behavior
On PC with 2 monitors, desktopCapturer.getSources return 2 screens. When change main screen, it show with title "Screen 1" secondary screen.

### Actual behavior
Method should correctly handle main screen switch and display with title "Screen 1" main screen.

### How to reproduce
[desktopCapturerScreenNumIssue.zip](https://github.com/electron/electron/files/1302236/desktopCapturerScreenNumIssue.zip)
atom/browser/api/atom_api_desktop_capturer.cc
}
void DesktopCapturer::OnSourceNameChanged(int index) {
}
void DesktopCapturer::OnSourceThumbnailChanged(int index) {
}
bool DesktopCapturer::OnRefreshFinished() {
  Emit("finished", media_list_->GetSources());
  return false;
}
mate::Handle<DesktopCapturer> DesktopCapturer::Create(v8::Isolate* isolate) {
  return mate::CreateHandle(isolate, new DesktopCapturer(isolate));
}
void DesktopCapturer::BuildPrototype(
    v8::Isolate* isolate, v8::Local<v8::FunctionTemplate> prototype) {
  prototype->SetClassName(mate::StringToV8(isolate, "DesktopCapturer"));
  mate::ObjectTemplateBuilder(isolate, prototype->PrototypeTemplate())
      .SetMethod("startHandling", &DesktopCapturer::StartHandling);
}
}  
}  
namespace {
void Initialize(v8::Local<v8::Object> exports, v8::Local<v8::Value> unused,
                v8::Local<v8::Context> context, void* priv) {
  v8::Isolate* isolate = context->GetIsolate();
  mate::Dictionary dict(isolate, exports);
  dict.Set("desktopCapturer", atom::api::DesktopCapturer::Create(isolate));
}
}  
NODE_MODULE_CONTEXT_AWARE_BUILTIN(atom_browser_desktop_capturer, Initialize);