Glimpse: Optimize mapEachRow a little bit

Avoid getting column indexes for each element, save it inside an array
which gets passed to the mapping callback.
Could've went with a (hashed) map of string to int, but it defeats the
purpose, array access is O(1)

Change-Id: I0ad8f3585abe2ab6a2ae42c864a896e29362fff6
3 files changed