function MapBookKeeping(mapResult, keyPrefix, mapFunction, mapContext) {
	  this.result = mapResult;
	  this.keyPrefix = keyPrefix;
	  this.func = mapFunction;
	  this.context = mapContext;
	  this.count = 0;
	}
PooledClass representing the bookkeeping associated with performing a child
mapping. Allows avoiding binding callbacks.

@constructor MapBookKeeping
@param {!*} mapResult Object containing the ordered map of results.
@param {!function} mapFunction Function to perform mapping with.
@param {?*} mapContext Context to perform mapping with.