An object representing an action in the media notification. Note that it can be either a pre-defined action or a custom action. To create an action, use NotificationAction.Builder. If the action is a pre-defined action, only NotificationAction.Builder.setAction(String) needs to be called. See MediaIntentReceiver for the list of pre-defined actions. If the action is a custom action, call NotificationAction.Builder.setAction(String) to set the action, NotificationAction.Builder.setIconResId(int) to set the icon's resource ID, and NotificationAction.Builder.setContentDescription(String) to set the content description for accessibility.