Merge "Adding get_ref_frame_buffer() function."

diff --cc vp9/encoder/vp9_encodeframe.c
Simple merge

diff --cc vp9/encoder/vp9_firstpass.c
Simple merge

diff --cc vp9/encoder/vp9_onyx_int.h
Simple merge

diff --cc vp9/encoder/vp9_rdopt.c
Simple merge