To control google map boundary, you should use After map pans(users drag and drop to move map) , we should verify if new map center is still in the bound.
Below link shows world map boundary:
However if you use this bounds to verify it's center, like this:
You will get "false".
Blow blog also mentioned this issue:
I finally realise that, the constructor of LatLngBounds() use south-west and north-east corners: