Continuation<TResult, TContinuationResult>	A function that is called to continue execution after completion of a`Task`.
OnCanceledListener	Listener called when a`Task`is canceled.
OnCompleteListener<TResult>	Listener called when a`Task` completes.
OnFailureListener	Listener called when a`Task`fails with an exception.
OnSuccessListener<TResult>	Listener called when a`Task`completes successfully.
OnTokenCanceledListener	Listener called when a`CancellationToken` is canceled successfully.
SuccessContinuation<TResult, TContinuationResult>	A function that is called to continue execution then a`Task` succeeds.

CancellationToken	Propagates notification that operations should be canceled.
CancellationTokenSource	Creates a new`CancellationToken` or cancels one that has already created.
Task<TResult>	Represents an asynchronous operation.
TaskCompletionSource<TResult>	Provides the ability to create`Task`-based APIs.
TaskExecutors	Standard`Executor` instances for use with`Task`.
Tasks	`Task`utility methods.

DuplicateTaskCompletionException	An exception indicating that something attempted to set a result, exception, or cancellation on a`Task`that was already completed.
RuntimeExecutionException	Runtime version of`ExecutionException`.

com.google.android.gms.tasks