Available only in the v=beta channel: https://goo.gle/3oAthT3.
The visible region of the map. Returns null if the map has
no size. Returns null if the OverlayView is on a
StreetViewPanorama.
The width of the world in pixels in the current zoom level. For
projections with a heading angle of either 90 or 270 degrees, this
corresponds to the pixel span in the Y-axis.
This object is made available to the
OverlayView
from within the draw method. It is not guaranteed to be initialized until draw is called.