Turn on frame_sign_bias by default.

This experiment of frame_sign_bias is to remove the 7 bits in the
frame header that signal the sign bias value for the 7 reference
frames. Instead of explicit signaling, this experiment is to use
the frame_offset value to derive the frame sign bias. It achieves
-0.08~-0.1% coding gain on average. It has been adopted by AOM.

Change-Id: I543f2641d9a11cabfe822cd4daa8b88b938421d6

build/cmake/aom_config_defaults.cmake

diff --git a/build/cmake/aom_config_defaults.cmake b/build/cmake/aom_config_defaults.cmake
index 6218db0..942a87b 100644
--- a/build/cmake/aom_config_defaults.cmake
+++ b/build/cmake/aom_config_defaults.cmake
@@ -142,7 +142,7 @@
 set(CONFIG_FILTER_INTRA 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_FP_MB_STATS 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_FRAME_MARKER 1 CACHE NUMBER "AV1 experiment flag.")
-set(CONFIG_FRAME_SIGN_BIAS 0 CACHE NUMBER "AV1 experiment flag.")
+set(CONFIG_FRAME_SIGN_BIAS 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_FRAME_SIZE 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_FWD_KF 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_HASH_ME 0 CACHE NUMBER "AV1 experiment flag.")

configure

diff --git a/configure b/configure
index cc62ab4..c8348cf 100755
--- a/configure
+++ b/configure
@@ -517,6 +517,7 @@
     soft_enable rect_tx_ext_intra
     soft_enable filter_intra
     soft_enable ext_skip
+    soft_enable frame_sign_bias
     soft_enable ext_warped_motion
     soft_enable horzonly_frame_superres