RefBase subclasses can now decide how they want to be destroyed.

This adds a destroy() virtual on RefBase which
sublasses can implement. destroy() is called
in lieu of the destructor whenthe last strong
ref goes away.

Bug: 4483050
Change-Id: I8cbf6044a6fd3f01043a45592b5a60fa1e5fade2
diff --git a/include/utils/RefBase.h b/include/utils/RefBase.h
index c24c0db..1b4a310 100644
--- a/include/utils/RefBase.h
+++ b/include/utils/RefBase.h
@@ -115,7 +115,14 @@
 protected:
                             RefBase();
     virtual                 ~RefBase();
-    
+
+    // called when the last reference goes away. this is responsible for
+    // calling the destructor. The default implementation just does
+    // "delete this;".
+    // Make sure to never acquire a strong reference from this function. The
+    // same restrictions than for destructors apply.
+    virtual void            destroy() const;
+
     //! Flags for extendObjectLifetime()
     enum {
         OBJECT_LIFETIME_WEAK    = 0x0001,