logd: make LogBuffer an interface

We may use different implementations of LogBuffer in the future, so we
make it interface and create a concrete ChattyLogBuffer class that
implements it.

Test: logging unit tests
Change-Id: I5731d6404640664c9acc26b7c677dff3110c6a11
diff --git a/logd/LogKlog.cpp b/logd/LogKlog.cpp
index 5242dc3..1ea87a9 100644
--- a/logd/LogKlog.cpp
+++ b/logd/LogKlog.cpp
@@ -767,7 +767,7 @@
     }
 
     // Log message
-    int rc = logbuf->log(LOG_ID_KERNEL, now, uid, pid, tid, newstr, (uint16_t)n);
+    int rc = logbuf->Log(LOG_ID_KERNEL, now, uid, pid, tid, newstr, (uint16_t)n);
 
     return rc;
 }