Fix compatibility issues in XmlPullParserFactory.

- We should set features on a parser only if the feature
  value is true. I.e, we guarantee that we'll never call
  XmlPullParser.setFeature(..., false).

- In change 0363556bad8930a, we didn't consider the fact
  that apps could extend XmlPullParserFactory and modify
  protected fields to change the parser / serializer that's
  instantiated. I've reinstated this feature, despite the
  fact that it's a particularly pointless feature on a
  more-or-less pointless public API. Apps can and should
  instantiate their own parser instances directly instead
  of going through this factory.

bug: 12956724

Change-Id: I793eba335b5385eb641e023b3613bba4515a85bf
2 files changed