The compiler cannot deduce the type of ComponentRenderer as long as the syntax has errors. I guess your error is in during creation of Html component for the column header. Please try to remove the setHeader(..) part and check if the ComponentRenderer still shows up wrong.
The error in the Html component is the mix-up of double-quotes. You can for example use single quotes for inside the actual html code
→ new Html("<font face='SansSerif'>").
I’m also pretty sure the actual html code of yours is not valid too. In addition, I recommend not using Vaadins Html component, if you can also use a Span or a Div. Html has some drawbacks and issues.