nl_tokens: Exponential backoff strategy .
pl_tokens: function ExponentialBackoffStrategy ( options ) { BackoffStrategy . call ( this , options ) ; this . backoffDelay_ = 0 ; this . nextBackoffDelay_ = this . getInitialDelay ( ) ; this . factor_ = ExponentialBackoffStrategy . DEFAULT_FACTOR ; if ( options && options . factor !== undefined ) { precond . checkArgument ( <mask> . factor > 1 , 'Exponential factor should be greater than 1 but got %s.' , options . factor ) ; this . factor_ = options . factor ; } }