Include oom_adjust reason in trace

Enumerated a few reasons for calling updateOomAdjust() in
order to trace how long and how often oom_adj was being
re-evaluated for the different reasons.

Bug: 123043091
Test: run systrace and view the output
Change-Id: I4d3f7946531e9477b0f090e07615b29777b19fa5
6 files changed