Calling resize by it self will not acheive what you need.
What you need to do is first (before a resize occurs) get the current center of the map
var currCenter = map.getCenter();
Then you need to do something like the following, after your div is resized.
google.maps.event.trigger(map, 'resize');
map.setCenter(currCenter);
Should do the trick
UPDATE 2018-05-22
With a new renderer release in version 3.32 of Maps JavaScript API the resize event is no longer a part of Map class.
The documentation states
When the map is resized, the map center is fixed
The full-screen control now preserves center.
There is no longer any need to trigger the resize event manually.
source: https://developers.google.com/maps/documentation/javascript/new-renderer
google.maps.event.trigger(map, "resize"); doesn’t have any effect starting from version 3.32