logd: separate LogStatistics from LogBuffer
LogStatistics is intertwined with LogBuffer, even relying on it for
thread safety. This needs to change to have a proper
LogBufferInterface, so this CL separates them. Specifically:
1) Adding a lock to LogStatistics and adding thread annotations to
ensure that data structures are protected appropriately.
2) Moving prune_rows calculation into LogStatistics so it is done
while holding this lock.
3) Using LogStatistics instead of LogBuffer where appropriate.
Note that there should not be a significant performance regression
with this lock, as it will almost always been uncontended. If
anything, it should alleviate pressure from LogBuffer's lock.
Test: logging unit tests
Change-Id: I9d6dde2c96c9f024fa0341711c7bc63379e8e406
17 files changed