logd: optimize statistics

- Go back to basic requirements
- Simplify
- use hash tables to minimize memory impact

Bug: 19608965
Change-Id: If7becb34354d6415e5c387ecea7d4109a15259c8
diff --git a/logd/LogBuffer.h b/logd/LogBuffer.h
index 13e6aa8..a29e015 100644
--- a/logd/LogBuffer.h
+++ b/logd/LogBuffer.h
@@ -78,7 +78,7 @@
 private:
     void maybePrune(log_id_t id);
     void prune(log_id_t id, unsigned long pruneRows, uid_t uid = AID_ROOT);
-
+    LogBufferElementCollection::iterator erase(LogBufferElementCollection::iterator it);
 };
 
 #endif // _LOGD_LOG_BUFFER_H__