Cache least recently used output buffer.

- reduce memory allocations especially when Xml is serialized inside a
tight inner loop,
- performance slightly improved.

BEFORE:
100 packages:
[2/4] android.util.XmlPerfTest#timeWrite_Binary: PASSED (10.516s)
	timeWrite_Binary_mean: 674979
	threadAllocCount_mean: 59
	timeWrite_Binary_min: 671194
	timeWrite_Binary_median: 674798
	timeWrite_Binary_standardDeviation: 3658
	threadAllocSize_mean: 530176
10 packages:
[2/4] android.util.XmlPerfTest#timeWrite_Binary: PASSED (10.542s)
	timeWrite_Binary_mean: 71113
	threadAllocCount_mean: 56
	timeWrite_Binary_min: 70201
	timeWrite_Binary_median: 71237
	timeWrite_Binary_standardDeviation: 692
	threadAllocSize_mean: 59136
1 package:
[2/4] android.util.XmlPerfTest#timeWrite_Binary: PASSED (10.091s)
	timeWrite_Binary_mean: 15698
	threadAllocCount_mean: 56
	timeWrite_Binary_min: 15072
	timeWrite_Binary_median: 15677
	timeWrite_Binary_standardDeviation: 410
	threadAllocSize_mean: 6439

AFTER:
100 packages:
[1/1] android.util.XmlPerfTest#timeWrite_Binary: PASSED (10.221s)
	timeWrite_Binary_mean: 605862
	threadAllocCount_mean: 53
	timeWrite_Binary_min: 602353
	timeWrite_Binary_median: 604424
	timeWrite_Binary_standardDeviation: 4972
	threadAllocSize_mean: 492748
10 packages:
[1/1] android.util.XmlPerfTest#timeWrite_Binary: PASSED (10.575s)
	timeWrite_Binary_mean: 58710
	threadAllocCount_mean: 50
	timeWrite_Binary_min: 57551
	timeWrite_Binary_median: 57798
	timeWrite_Binary_standardDeviation: 2129
	threadAllocSize_mean: 21696
1 package:
[1/1] android.util.XmlPerfTest#timeWrite_Binary: PASSED (10.151s)
	timeWrite_Binary_mean: 11576
	threadAllocCount_mean: 50
	timeWrite_Binary_min: 11315
	timeWrite_Binary_median: 11381
	timeWrite_Binary_standardDeviation: 431
	threadAllocSize_mean: 4336

Test: atest FastDataPerfTest XmlPerfTest
Bug: 195994150
Fixes: 195994150

Merged-In: Ieedd27a676d718967c2fac30bc48a68ae636a180
Change-Id: Ieedd27a676d718967c2fac30bc48a68ae636a180