commit a912c6ec314d816767a4c3eb4e5e1bddcc4c1186
author Zoe Liu <zoeliu@google.com> Thu May 05 17:32:51 2016 -0700
committer Zoe Liu <zoeliu@google.com> Sat May 07 00:27:51 2016 -0700
tree f2b6712c08bab8150f0a92e0709a37f7d28a74f9
parent bd33326372073c49b01df244543c42470e3308b6

Make LAST_FRAME always point to the newly coded frame in ext-refs

This patch changes the encoder only for the ext-refs experiment. For
each newly coded frame to refresh the LAST_FRAME, the decoder is
notified that the LAST4_FRAME is to be refreshed, and read out the
updated reference frame buffer vitural indexes for the next coded
frame in a way that:
LAST4_FRAME => LAST_FRAME,
LAST_FRAME  => LAST2_FRAME,
LAST2_FRAME => LAST3_FRAME, and
LAST3_FRAME => LAST4_FRAME.

Compared against the original ext-refs experiment in TOT, a small gain
is achieved in overall PSNR:
lowres Avg: -0.154
lowres BDRate: -0.044

Change-Id: I648810c146a3cd915b408274a9373b7d38324864