The Resources panel should show the total non-overlapping latency for all the resource loads on the page. This number would give developers a good idea how much time is wasted waiting for data from the server.
Closing as invalid, as this bug pertains to the old inspector UI and/or its tests. Please file a new bug (https://www.webkit.org/new-inspector-bug) if the bug/feature/issue is still relevant to WebKit trunk.