Make GraphicBuffer a RefBase

- this gives us access to RefBase's refcounting debugging
- it doesn't cost much because GraphicBuffer already has a vtable

Change-Id: I7f696e421fea14b14bfaeb83880689b83e96af4d
diff --git a/include/ui/GraphicBuffer.h b/include/ui/GraphicBuffer.h
index 4b9b5a8..ea9368d 100644
--- a/include/ui/GraphicBuffer.h
+++ b/include/ui/GraphicBuffer.h
@@ -24,6 +24,7 @@
 #include <ui/PixelFormat.h>
 #include <ui/Rect.h>
 #include <utils/Flattenable.h>
+#include <utils/RefBase.h>
 
 
 struct ANativeWindowBuffer;
@@ -37,10 +38,8 @@
 // ===========================================================================
 
 class GraphicBuffer
-    : public ANativeObjectBase<
-        ANativeWindowBuffer,
-        GraphicBuffer, 
-        LightRefBase<GraphicBuffer> >, public Flattenable
+    : public ANativeObjectBase< ANativeWindowBuffer, GraphicBuffer, RefBase >,
+      public Flattenable
 {
 public: