logd: Worst Tag filter enabled for events buffer

- Add drop logistics to TagTable
- replace uid references to a key reference since it
  is an UID for most buffers, but a TAG for the
  events and security buffer
- template the find worst entry mechanics into LogFindWorst class

Bug: 30118730
Change-Id: Ibea4be2c50d6ff4b39039e371365fed2453f17a2
diff --git a/logd/LogBuffer.h b/logd/LogBuffer.h
index 7e99236..b390a0c 100644
--- a/logd/LogBuffer.h
+++ b/logd/LogBuffer.h
@@ -89,7 +89,7 @@
     typedef std::unordered_map<uid_t,
                                LogBufferElementCollection::iterator>
                 LogBufferIteratorMap;
-    LogBufferIteratorMap mLastWorstUid[LOG_ID_MAX];
+    LogBufferIteratorMap mLastWorst[LOG_ID_MAX];
     // watermark of any worst/chatty pid of system processing
     typedef std::unordered_map<pid_t,
                                LogBufferElementCollection::iterator>