Merge "Add max burst bitrate control."

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

diff --cc vp9/encoder/vp9_onyx_if.c
Simple merge

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

diff --cc vp9/encoder/vp9_ratectrl.c
Simple merge