UKM entry names are often duplicated between the generated code and client code.

We generate the names as kEntryName member of the builder class. However, lots of code currently declares these separately too.

Now, it may be that these get de-duped by compilers/linkers, but it would be better if there was no duplication in the source code and the logging code just referenced kEntryName.

e.g.

https://cs.chromium.org/search/?q=LocalNetworkRequests%5C%22&type=cs

We should also advise the same during code review.