I see an example in Longman dictionary. For the word of "toolbar", it says, "a row of small pictures at the top of a computer screen that allow you to do particular things in a document". I am confused about it. The subject is "a row of small pictures" while its clause goes like "that allow you..." I think it should be like "that allows you..." Being a famous dictionary, it should be grammatical correct, even when offering a phrase instead of a complete sentence. I see in some small dictionary, an example is, "The first row alone consists of five rooms." Why Longman dictionary says that way?
A row is singular, but small pictures is plural, and because it is the small pictures that are allowing you to take the action, you use "allow."
Likewise, we could expand your second sentence as follows:
The first row alone consists of five rooms that contain tables and chairs.
Consists refers back to row, which is singular, but contain refers back to rooms, which is plural.