Use Monitor in quantile hist.

[trivialfis]

Now that we published r0.82, old performance monitor can be safely removed. Small example of output:

[23:37:34] ======== Monitor: Learner ========
[23:37:34] EvalOneIter: 0.000541892s, 16 calls @ 33us
[23:37:34] GetGradient: 0.00054553s, 16 calls @ 34us
[23:37:34] PredictRaw: 0.00403017s, 16 calls @ 251us
[23:37:34] UpdateOneIter: 11.6501s, 16 calls @ 728131us
[23:37:34] ======== Monitor: GBTree ========
[23:37:34] BoostNewTrees: 11.6216s, 16 calls @ 726351us
[23:37:34] CommitModel: 0.0238338s, 16 calls @ 1489us
[23:37:34] ======== Monitor: Quantile::Builder ========
[23:37:34] ApplySplit: 0.0314834s, 1704 calls @ 18us
[23:37:34] BuildHist: 2.7814s, 1736 calls @ 1602us
[23:37:34] BuildLocalHistograms: 4.62041s, 224 calls @ 20626us
[23:37:34] BuildNodeStats: 0.00127785s, 224 calls @ 5us
[23:37:34] EvaluateSplit: 3.5262s, 3440 calls @ 1025us
[23:37:34] InitData: 0.00167754s, 32 calls @ 52us
[23:37:34] InitNewNode: 0.000792078s, 3440 calls @ 0us
[23:37:34] SubtractionTrick: 1.6663s, 1704 calls @ 977us
[23:37:34] SyncHistograms: 3.0806s, 224 calls @ 13752us
[23:37:34] Update: 11.2678s, 32 calls @ 352118us
[23:37:34] ======== Monitor: QuantileHist ========
[23:37:34] ======== Monitor: HistCutMatrix ========
[23:37:34] Init: 0.264822s, 1 calls @ 264821us
Finished training,  11.686916589736938

[hcho3]

@trivialfis Could you provide more context? What is the difference between "old" and "new" monitor classes?

[trivialfis]

@hcho3 Originally discussed in: #4102 (comment) . After this release performance reporting utilities should be unified.