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

/cc @alespergl 
atom/common/api/atom_api_native_image.cc
const gfx::Rect& rect) {
  gfx::ImageSkia cropped = gfx::ImageSkiaOperations::ExtractSubset(
      image_.AsImageSkia(), rect);
  return mate::CreateHandle(isolate,
                            new NativeImage(isolate, gfx::Image(cropped)));
}
void NativeImage::AddRepresentation(const mate::Dictionary& options) {
  int width = 0;
  int height = 0;
  float scale_factor = 1.0f;
  options.Get("width", &width);
  options.Get("height", &height);
  options.Get("scaleFactor", &scale_factor);
  bool skia_rep_added = false;
  gfx::ImageSkia image_skia = image_.AsImageSkia();