libutils: hide SharedBuffer by moving SharedBuffer.h to the implementation directory

Some methods in header files of classes using SharedBuffer need
to be moved to the implementation files accordingly

Change-Id: I891f3ace2b940ab219e4e449040bfed71c0547db
diff --git a/libutils/SharedBuffer.cpp b/libutils/SharedBuffer.cpp
index 3555fb7..003e386 100644
--- a/libutils/SharedBuffer.cpp
+++ b/libutils/SharedBuffer.cpp
@@ -17,9 +17,10 @@
 #include <stdlib.h>
 #include <string.h>
 
-#include <utils/SharedBuffer.h>
 #include <utils/Atomic.h>
 
+#include "SharedBuffer.h"
+
 // ---------------------------------------------------------------------------
 
 namespace android {