Merge changes from topic "CacheOomRanker-new-features-sc-qpr1-dev" into sc-qpr1-dev

* changes:
  Use Process.getRss instead of mProfile.getLastRss in CacheOomRanker.
  Change CacheOomRanker's "uses" feature.
  Fix race condition when using mPreserveTopNApps.
  Allow CacheOomRanker to rerank when there's <8 processes in the cache.
  Fix CacheOomRankerTest.