This might be a fringe case, since not many people will be using chromebooks. But on mine, I cannot zoom into a map without connecting an external mouse. Pinching the touchpad zooms in the entire page, and there’s no dedicated + button (only shift & =). Once I’ve zoomed out of a map, I’m stuck there.
An optional on-screen “+” and “-” zoom panel (that you can turn off from settings) would be a solution that does not unecessarily clutter the UI of those who don’t need it.