DO NOT MERGE ANYWHERE: ImageReader: Add discardFreeBuffers method am: e175aa82b5  -s ours am: 7d99482be5  -s ours am: ca7e060945  -s ours am: 05274a5ab0  -s ours
am: bd6d44c417  -s ours

Change-Id: Idade786dfcbcc2b65565489a218d0fc63c0c7d2b