IPlayer has weak reference to PlayerBase

The implementation of the IPlayer interface was an inner class
  that implicitly held a strong reference to the PlayerBase
  instance, preventing subclasses of PlayerBase to be GC'd.
The fix consists in making the IPlayer implementation be a static
  class and hold a weak reference to PlayerBase.

Test: see bug
Bug: 35359144
Change-Id: I5f7d658f4bda07c92cfdb437b42d3f78213ab552