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/renderer/atom_renderer_client.cc
blink::WebSpeechSynthesizerClient* client) {
  return new TtsDispatcher(client);
}
bool AtomRendererClient::OverrideCreatePlugin(
    content::RenderFrame* render_frame,
    blink::WebLocalFrame* frame,
    const blink::WebPluginParams& params,
    blink::WebPlugin** plugin) {
  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
  if (params.mimeType.utf8() == content::kBrowserPluginMimeType ||
      command_line->HasSwitch(switches::kEnablePlugins))
    return false;
  *plugin = nullptr;
  return true;
}
void AtomRendererClient::DidCreateScriptContext(