logd: replace stats.add+stats.subtract with stats.addTotal

Replace stats.add(elem) + stats.subtract(elem) with a new more
efficient method stats.addTotal(elem).

Test: gTest liblog-unit-test, logd-unit-tests and logcat-unit-tests
Bug: 37254265
Change-Id: I2b3c2ac44209772b38f383ae46fe6c4422b542cf
3 files changed