@GuardedBy("this")
  @VisibleForTesting
  @Nullable
  CloseableReference<MemoryChunk> getCloseableReference() {
    return mBufRef;
  }
Validates that the ByteBuffer instance is valid (aka not closed). If it is closed, then we
raise a ClosedException This doesn't really need to be synchronized, but lint won't shut up
otherwise

@throws ClosedException
imagepipeline/src/main/java/com/facebook/imagepipeline/memory/MemoryPooledByteBuffer.java