this bug was introduced recently. it caused RefBase's weakref_impl
structure to be leaked for every RefBase object (about 20 bytes).
Change-Id: Ia9b155fbfa643ef72cfb8129e96260a3b806a78c
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