Make MemoryDealer's destructor protected instead of public.

MemoryDealer, like all other subclasses of RefBase,MUST NOT BE stack-allocated, a protected destructor prohibits stack-allocation while allowing the baseclass to properly invoke the subclass' destructor once the refcount drops to 0.

include/binder/MemoryDealer.h

@@ -218,8 +218,6 @@ public:
             const sp<HeapInterface>& heap,
             const sp<AllocatorInterface>& allocator);
 
-    virtual ~MemoryDealer();
-
     virtual sp<IMemory> allocate(size_t size, uint32_t flags = 0);
     virtual void        deallocate(size_t offset);
     virtual void        dump(const char* what, uint32_t flags = 0) const;
@@ -228,6 +226,9 @@ public:
     sp<IMemoryHeap> getMemoryHeap() const { return heap(); }
     sp<AllocatorInterface> getAllocator() const { return allocator(); }
 
+protected:
+    virtual ~MemoryDealer();
+
 private:    
     const sp<HeapInterface>&        heap() const;
     const sp<AllocatorInterface>&   allocator() const;