Investigate Shadow DOM performance

We should investigate how Shadow DOM performs in such scenarios:

1. First render of the page
2. Adding more elements to the page
3. Page is resized

We should compare the following scenarios with matching CSS to the page without Shadow DOM. The difference should indicate the performance overhead that Shadow DOM brigs. Test cases could use a diff file list as a testing bench. The tests should be performed on different amounts of HTML: 1 file, 10 files, 100 files.

The results should help us decide on the style isolation strategy for Rapid Diffs.