Revert "revert surfaceflinger leak fix as it uncovered a crasher on xoom"

This reverts commit af6edba59e250adbdfa5b3c3be134f70d8c38a16.

Change-Id: I7793d3ca8a4d20a2b188364f47854328ab5f586d
diff --git a/include/utils/RefBase.h b/include/utils/RefBase.h
index a21a18b..ca17082 100644
--- a/include/utils/RefBase.h
+++ b/include/utils/RefBase.h
@@ -116,6 +116,20 @@
 
     typedef RefBase basetype;
 
+    // used to override the RefBase destruction.
+    class Destroyer {
+        friend class RefBase;
+        friend class weakref_type;
+    public:
+        virtual ~Destroyer();
+    private:
+        virtual void destroy(RefBase const* base) = 0;
+    };
+
+    // Make sure to never acquire a strong reference from this function. The
+    // same restrictions than for destructors apply.
+    void setDestroyer(Destroyer* destroyer);
+
 protected:
                             RefBase();
     virtual                 ~RefBase();