logd: switch asprintf to std::string

Bug: 23350706
Change-Id: I715cdd4563a09de3680081947a3439f0cac623be
diff --git a/logd/LogStatistics.h b/logd/LogStatistics.h
index 760d6b2..61000d2 100644
--- a/logd/LogStatistics.h
+++ b/logd/LogStatistics.h
@@ -331,8 +331,7 @@
     size_t sizesTotal(log_id_t id) const { return mSizesTotal[id]; }
     size_t elementsTotal(log_id_t id) const { return mElementsTotal[id]; }
 
-    // *strp = malloc, balance with free
-    void format(char **strp, uid_t uid, unsigned int logMask);
+    std::string format(uid_t uid, unsigned int logMask);
 
     // helper (must be locked directly or implicitly by mLogElementsLock)
     char *pidToName(pid_t pid);