LatLngBounds.contains()

Returns true if the given lat/lng is in this bounds.

map.getVisibleRegion(function(latLngBounds) {
  var point = new plugin.google.maps.LatLng(0, 0);
  var isContained = latLngBounds.contains(point);
  alert(point.toUrlValue() + " is" + (isContained ? " " : " not ") + " contained in this bounds.");
});