**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
BOUNCE_CRITICAL = 0,
    BOUNCE_INFORMATIONAL = 10,
  };
  int DockBounce(BounceType type);
  void DockCancelBounce(int request_id);
  
  void DockDownloadFinished(const std::string& filePath);
  
  void DockSetBadgeText(const std::string& label);
  std::string DockGetBadgeText();
  
  void DockHide();
  void DockShow();
  bool DockIsVisible();
  
  void DockSetMenu(AtomMenuModel* model);
  
  void DockSetIcon(const gfx::Image& image);