**Is your feature request related to a problem? Please describe.**
The following cause a bad effect with the window appearing/exploding (glitch?) from top-left :
```
//user clicks on tray-icon => context-menu => show and I'm supposed to pop-up the app window
app.dock.show();
window.show();
```
This happens because app.dock.show() is not synchronous thus genie effect from the dockbar can't take place because the dock icon is not yet created when we call window.show().

**Describe the solution you'd like**
app.dock.show() should return a promise fullfilled when the icon is in the dock.

**Describe alternatives you've considered**
Right now I'm doing this and it works:
```
app.dock.show();
app.dock.setIcon(appIcon);
setTimeout(window.show, 500);
```

Another is to provide a way to disable system animation (OSX) for window.show() / window.hide().

**Additional context**
Of course I have no idea about internal API availability/functionality. If not possible we can just close this issue and other people will have a reference about it! :)
atom/browser/browser.h
class Browser : public WindowListObserver {
 public:
  Browser();
  ~Browser() override;
  static Browser* Get();
  
  void Quit();
  
  void Exit(mate::Arguments* args);
  
  void Shutdown();
  
  void Focus();
  
  std::string GetVersion() const;
  
  void SetVersion(const std::string& version);
  
  std::string GetName() const;
  
  void SetName(const std::string& name);
  
  void AddRecentDocument(const base::FilePath& path);
  
  void ClearRecentDocuments();
  
  void SetAppUserModelID(const base::string16& name);