This is an umbrella bug for improving keyboard-only navigation in Web Inspector.
It seems impossible to switch between the DOM pane and the Styles pane with the keyboard.
Related: https://bugs.webkit.org/show_bug.cgi?id=33126
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.