It doesn't look very good for "native" apps to overscroll when scrolling. Would be nice to have a BrowserWindow option to disable overscroll

![untitled12](https://cloud.githubusercontent.com/assets/170270/15033357/fc36e32e-1293-11e6-8cdc-6c17b0f504dd.gif)
## 
- Electron version: 0.37.8
- Operating system: OS X 10.11.4

atom/browser/web_contents_preferences.cc
web_preferences_.MergeDictionary(&extend);
}
content::WebContents* WebContentsPreferences::GetWebContentsFromProcessID(
    int process_id) {
  for (WebContentsPreferences* preferences : instances_) {
    content::WebContents* web_contents = preferences->web_contents_;
    if (web_contents->GetRenderProcessHost()->GetID() == process_id)
      return web_contents;
  }
  return nullptr;
}
void WebContentsPreferences::AppendExtraCommandLineSwitches(
    content::WebContents* web_contents, base::CommandLine* command_line) {
  WebContentsPreferences* self = FromWebContents(web_contents);
  if (!self)
    return;
  base::DictionaryValue& web_preferences = self->web_preferences_;
  bool b;
#if defined(OS_WIN)
  
  if (web_preferences.GetBoolean(options::kDirectWrite, &b) && !b)
    command_line->AppendSwitch(::switches::kDisableDirectWrite);
#endif
  
  if (web_preferences.GetBoolean("plugins", &b) && b)
    command_line->AppendSwitch(switches::kEnablePlugins);