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

Change-Id: I46ae6bfb1d83053e7dd79a59f5b4b991df3bf97d