The debug connection is scoped to a tab/page. The page is a frame and may contain other frames. The protocol should make possible to: synchronously observe frame lifecycle, distinguish scripts from different frames, set breakpoint in a particular frame (but setting breakpoint on a similar script in all frames should be an important feature too), tell frame context that debugger stopped in, evaluate global expressions in a particular frame.
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.