am d81e9f88: am ddefdef5: Make ProGuard keep necessary members for serializable classes

Merge commit 'd81e9f88f4576dd8b18143f0a0d5f50c3758202b'

* commit 'd81e9f88f4576dd8b18143f0a0d5f50c3758202b':
  Make ProGuard keep necessary members for serializable classes