mesos/spark — pull request #584 by pwendell (2013-04-29 18:14:09+00:00)
Title: Spark-742: TaskMetrics should not employ per-record timing.

This patch does three things:

1. Makes TimedIterator a trait with two implementations (one a no-op)
2. Makes the default behavior to use the no-op implementation
3. Removes DelegateBlockFetchTracker. This is just cleanup, but it seems like
the triat doesn't really reduce complexity in any way.

In the future we can add other implementations, e.g. ones which perform sampling.