requestAds
Requests ads, if they have not already been requested. Must be called on the main thread.
Ads will be requested automatically when the player is prepared if this method has not been called, so it is only necessary to call this method if you want to request ads before preparing the player.
Parameters
adTagDataSpec
The data specification of the ad tag to load. See class javadoc for information about compatible ad tag formats.
adsId
A opaque identifier for the ad playback state across start/stop calls.
adViewGroup
A ViewGroup on top of the player that will show any ad UI, or
null if playing audio-only ads.