GMSOverlayLayer
@interface GMSOverlayLayer : CALayerGMSOverlayLayer is a custom subclass of CALayer, and an abstract baseclass for GMSOverlay
layers that allow custom animations.
Note that this CALayer or any subclass are never actually rendered directly, as GMSMapView is
provided entirely via an OpenGL layer. As such, adjustments or animations to ‘default’
properties of CALayer will not have any effect.
This is an implementation detail and it should not be instantiated directly.