They were disabled during the Chromium 61 upgrade. Fix them and enable.

/cc @alespergl 
atom/common/api/atom_api_native_image.cc
v8::Isolate* isolate, const GURL& url) {
  std::string mime_type, charset, data;
  if (net::DataURL::Parse(url, &mime_type, &charset, &data)) {
    if (mime_type == "image/png")
      return CreateFromPNG(isolate, data.c_str(), data.size());
    else if (mime_type == "image/jpeg")
      return CreateFromJPEG(isolate, data.c_str(), data.size());
  }
  return CreateEmpty(isolate);
}
#if !defined(OS_MACOSX)
mate::Handle<NativeImage> NativeImage::CreateFromNamedImage(
  mate::Arguments* args, const std::string& name) {
  return CreateEmpty(args->isolate());
}
#endif
/
void NativeImage::BuildPrototype(