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/LogBufferElement.cpp b/logd/LogBufferElement.cpp
index cc68ba4..32f641b 100644
--- a/logd/LogBufferElement.cpp
+++ b/logd/LogBufferElement.cpp
@@ -27,9 +27,9 @@
 #include <log/log_read.h>
 #include <private/android_logger.h>
 
-#include "LogBuffer.h"
 #include "LogCommand.h"
 #include "LogReader.h"
+#include "LogStatistics.h"
 #include "LogUtils.h"
 
 const uint64_t LogBufferElement::FLUSH_ERROR(0);