This is akin to how on Mac the traffic lights were not aligned with the tab content.  I believe in the end we centered the traffic lights within the vertical space instead of aligning them with the tab content.  Personally, I would have taken the other route, but whatever rationale we used there seems to apply here as well; and since these are currently vertically centered in the space, IMO this is WontFix.

The issue as I see it is that when there is only a single tab there is no visual indication of why the tab title, close button and new tab button are all slightly below centered relative to the window control buttons. Once there are multiple tabs the additional contrast between the tab and window background makes it clear that the tab strip and window controls are part of separate UI control sets.

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That's a fair critique.  I think adding the divider between the close button and new tab button will help a little here because it will make the strip feel a tiny bit more like a tabstrip.  I'm not sure there's a lot we can do, however.  The naive answer -- center the text within the entire above-toolbar region when in single tab mode -- is problematic because e.g. inactive windows don't draw single-tab mode, so just activating a different window would cause the text to move up and down.

Naive rebuttal: Why don't inactive tabs draw single-tab mode? :)

Additionally, why do we draw a close tab button in single-tab mode if it's redundant with the window close button?

So there's any visual distinction between active and inactive windows, which could otherwise be done with frame color changes.  I don't know how important that is on CrOS, but it's important on Windows.

The close button in single tab mode is contentious; Alan wants to hide it until hover, I want to show it all the time, but in both cases the reason it's there is primarily for consistency, so that users can always close tabs the same way.  Imagine trying to close all three tabs in your window by hovering the first tab's close button and clicking three times.  It would work twice and then break, and you'd have to go click the window close button instead, which feels capricious.  Now, we could argue "people shouldn't close all the tabs one-by-one", but they do, and frequently, and until single-tab mode there wasn't any UI forcing them not to, so when we originally had no close button at all, we got (IMO justified) complaints.

Thanks for the feedback. We match the alignment of window controls as best as we can for each platform. Because they're different for each, the results are different for each so this is WAI. I'm going to mark this is as WontFix. 

Issues around single tab mode and it's respected controls can and will be addressed in their respected bugs under Proj-MdRefresh. Thanks!