I've been hearing about ideas for measuring code coverage in end-to-end tests (e.g., Selenium tests) and I really don't see a reason for that, even if this is technically feasible.
There's a concept of test pyramid that says that on the unit level you should have the highest number of tests, on integration level a medium number, and on end-to-end (Selenium) the smaller number of tests, because they are the hardest to maintain, the longest to execute and the least stable (because SUT is not isolated). So there's little chance you will cover all the code in end-to-end tests. Also, there might be areas in the lower layers of the code, which has not been exposed through, say, API so far (e.g., because the feature will be accessible in the next release), and can be tested only with unit tests.
I think the idea of Selenium or end-to-end test is to verify different business scenarios, so it is more about function/feature coverage.
Does measuring code coverage in end-to-end tests gives any value in addition to code coverage for unit tests?