Implement pending specs for ImageDownloaderAdapter::Base
user
```ruby
klass = ImageDownloaderAdapter::Base

describe klass do
  xit 'should download img tags with src in scheme http' do
  end

  xit 'should download img tags with src in scheme http' do
  end

  xit 'should download img tags with srcset in scheme http' do
  end

  xit 'should download img tags with src in scheme https' do
  end

  xit 'should download img tags with srcset in scheme https' do
  end

  xit 'should download img tags with embedded images' do
  end

  xit 'should download elements with background property in style attr' do
  end

  xit 'should download elements with background-image property in style attr' do
  end

  xit 'should download elements with background property in stylesheet' do
  end

  xit 'should download elements with background-image property in stylesheet' do
  end

  xit 'should download lazily loaded elements' do
  end
end
```
assistant