SlabinfoHelper: Initial Commit

SlabinfoHelper parses /proc/slabinfo and reports the rate of increase
or decrease in allocation sizes for each slab over the collection period. The rate is determined from the slope of a line fit to all samples collected between startCollecting and getMetrics. These metrics
are only useful over long (hours) test durations. Samples are taken once
per minute. getMetrics returns null for tests shorter than one minute.

Test: https://android-build.corp.google.com/test_investigate/?invocationId=I10200010190179925&testResultId=TR19728882730204231
Test: https://android-build.corp.google.com/test_investigate/?invocationId=I56700010189757710&testResultId=TR04128879169757459
Test: slabinfo.task_struct metric shows ~34x regression with known leak
Test: atest CollectorsHelperAospTest:com.android.helpers.tests.SlabinfoHelperTest

Change-Id: I080899710de972765405fe9a88834df544d0b776
4 files changed