I am trying to use the Android Device Monitor within Android Studio, but somehow I managed to remove all views.
I have tried resetting the perspectives, Window->Show Vie
I've experienced this same problem by using Window -> Reset Perspective. One should expect this to fix this issue, not break it. Go figure.
In any case, the DDMS workspace preferences are stored in %USERPROFILE%\.android\monitor-workspace
(e.g. C:\Users\my_user\.android\monitor-workspace
).
Just delete that folder and you're good to go.