Build summary does not show size diffs for chunks

See create-react-app issue #3048.

Steps to reproduce

1. git clone git@github.com:esturcke/cra-chunk-bundle-diff-bug.git
2. cd cra-chunk-bundle-diff-bug
3. yarn build
4. Comment out the first line of src/content.js and uncomment the second
5. yarn build

The build size after the second build does not show a difference in size for the chunk.