I tired with the offscreen mode and here are the problems I found:
- [x] <del>The `data` of `paint` event is empty when loading simple local pages.</del>
- [x] The size of `data` is wrong, current implement uses the size of pointer (`sizeof(bitmap_pixels)`).
- [x] Crashes when opening devtools for offscreen window.
- [x] We should probably show a dummy view indicating it is offscreen instead of provide NULL.
- [x] The offscreen window is affecting the rendering of other windows. Try running `./script/test.py -g offscreen` and then refreshing the window.

/cc @gerhardberger @brenca

atom/browser/api/atom_api_web_contents.cc
if (managed_web_contents()) {
    
    
    if (type_ == WEB_VIEW)
      guest_delegate_->Destroy();
    
    
    
    RenderViewDeleted(web_contents()->GetRenderViewHost());
    WebContentsDestroyed();
  }
}
bool WebContents::AddMessageToConsole(content::WebContents* source,
                                      int32_t level,
                                      const base::string16& message,
                                      int32_t line_no,
                                      const base::string16& source_id) {
  if (type_ == BROWSER_WINDOW || type_ == OFF_SCREEN) {
    return false;
  } else {
    Emit("console-message", level, message, line_no, source_id);
    return true;
  }
}
void WebContents::OnCreateWindow(const GURL& target_url,