Currently in WebKit, with a resource selected in the Resource view, the content of the selected resource is displayed. When you switch to the Timeline view, the content viewer remains. This feels counter-intuititive to what I would expect to have happen. I understand that prior to profiling in the Timeline view there is no "timeline" available for any given resource. In that case, the only potentially useful view is the content of the resource. That said, perhaps we could add an obvious label/button/dialog to prompt the user to start a new profile from within the content viewer while the Timeline view is activated and where no profile currently exists. A small banner at the top of the content viewer with an explanation along the lines of, "No profile exists for this resource" could be displayed. The banner could appear near the top of the content viewer in a manner similar to the "A problem occurred with this webpage so it reloaded" banner. It could also include an action button labeled something like "Start Profile" to begin profiling the page. These are clear directions providing an explanation for why the timeline is not showing and a prompt as an option for immediate action. This is especially useful guidance to developers new to the Web Inspector tools. Beyond that first scenario, once a profile is available, having a resource selected in the Resource view should mean that when you switch to the Timeline view, the selected resource should be visible (perhaps vertically centered for focus) and highlighted in the resource list with the timelines visible (no content view) and the resource's timeline highlighted as well. Clicking the resource to select it in the Timeline view could then activate the content viewer again. The "X" appears on the selected resource so that the content view can be closed again returning the user to the resource timeline viewer.
<rdar://problem/20116029>
I think the initial content for timelines is not great. It should have some sort of explanation of what to do. I don't think a banner is the right way to go. Instruments.app starts with a blank set of instruments and some instructions. As for auto-selecting the resource in currently shown timeline if it exists, I'm not exactly sure what new behavior you are proposing. A storyboard would be most helpful. We can whiteboard at the webkit meeting this week if you like.
Fixed by the tab based user interface as of: http://trac.webkit.org/changeset/183342