My preference is to add a "+" (open new window) to the overview page. This gives a nice touchable affordance, while ensuring that the overview page always has a reason to be shown.

I like the option of making it disabled when there's no window.
Alternative would be to have an empty state just like on Android but this seems less optimal.

re:#1, I'm assuming you mean new Chrome window? I'm not comfortable giving Chrome a special treatment over other apps in our system UI.

Adding Jenn in case she has any thoughts or preference.

What would it look like when disabled?

I would use the same rule as other system disabled system icon, reduce opacity to 38% and disable interactions (no ripple behind it, not sure if that's already the case, might be).

screenshot

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What if we reused this space for a "new browser window" button when there are no windows? Pros: no need to have a disabled button that does nothing when clicked. Cons: Same space does 2 different (but related and explainable, I feel) things depending on context.

If we didn't want to have a disabled button we could always just hide it. But I think it's better to reserve the space and have it disabled, much like disabled rows in a context menu.

+mccanny@ who is thinking about multi-window UX

My preference would be to have an empty state with text saying there are no open windows. Though it might seem obvious that there are no open windows, I think it pays to be explicit to the user, rather than having them work out the logic of why the button is disabled, or why it doesn't consistently open overview.

Removing the button for this case in touch mode would lead to frustration for users unintentionally opening the system menu in its place.

What is the best way to reach a decision here?

Re commend #12, what mccanny said in #11 is the approach we are proposing. We are working on exact visuals for the empty state. 
Something we are considering at the moment is an illustration that comes with the wording mentioned due to the large empty screen real-estate that gets user lost.

removing from my queue until design has a proposal.

Re comment #11 and #13 - are you suggesting text for a tooltip/hint? We don't expect to have a mouse cursor in touchview.

I'm concerned that removing the control will add some confusion to the interface. Are we intending to make better use of that space?

any updates?

This is now fixed with the updated overview visuals + empty state: crbug.com/782320