ically generated from the tree. The histogram
     * names are of the form
     *   "${cpuTime|cpuPercentage}:${processType}:${threadType}:" +
     *   "${railStage}:${railStageInitiator}"
     *
     * cpuTime histograms contain total consumed cpu time, while cpuPercentage
     * histograms contain cpu time as a percentage of wall time. In multicore
     * situations, this percentage can be larger than 100.
     *
     * @param {!tr.b.MultiDimensionalViewNode} rootNode
     * @param {!tr.v.HistogramSet} hi