Add experiment of 'frame_refs'

The target of this experiment is to fix and develop bitstream syntax
changes related to reference frames, especially considering:
(1) Fix various issues in aomedia bug 973;
(2) Make according changes accomondating the adoption of frame_marker.

BUG=aomedia:973

Change-Id: Ia8731eaa3b3d2cdacbbe3c12b0793ac15928c054

build/cmake/aom_config_defaults.cmake

diff --git a/build/cmake/aom_config_defaults.cmake b/build/cmake/aom_config_defaults.cmake
index 60a323c..151e0b6 100644
--- a/build/cmake/aom_config_defaults.cmake
+++ b/build/cmake/aom_config_defaults.cmake
@@ -147,6 +147,7 @@
 set(CONFIG_FILTER_INTRA 0 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_REFS 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_FRAME_SIGN_BIAS 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_FRAME_SIZE 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_FRAME_SUPERRES 0 CACHE NUMBER "AV1 experiment flag.")

build/cmake/aom_experiment_deps.cmake

diff --git a/build/cmake/aom_experiment_deps.cmake b/build/cmake/aom_experiment_deps.cmake
index e7fdfe8..693108c 100644
--- a/build/cmake/aom_experiment_deps.cmake
+++ b/build/cmake/aom_experiment_deps.cmake
@@ -75,6 +75,12 @@
     endif ()
   endif ()
 
+  if (CONFIG_FRAME_REFS)
+    if (NOT CONFIG_FRAME_MARKER)
+	    change_config_and_warn(CONFIG_FRAME_MARKER 1 CONFIG_FRAME_REFS)
+    endif ()
+  endif ()
+
   if (CONFIG_FRAME_SIGN_BIAS)
     if (NOT CONFIG_FRAME_MARKER)
       change_config_and_warn(CONFIG_FRAME_MARKER 1 CONFIG_FRAME_SIGN_BIAS)

configure

diff --git a/configure b/configure
index c7902dd..a5f96db 100755
--- a/configure
+++ b/configure
@@ -324,6 +324,7 @@
     mfmv
     frame_marker
     jnt_comp
+    frame_refs
     frame_sign_bias
     ext_skip
     obu
@@ -548,6 +549,7 @@
     enabled cdef_singlepass && enable_feature cdef
     enabled mfmv && enable_feature frame_marker
     enabled jnt_comp && enable_feature frame_marker
+    enabled frame_refs && enable_feature frame_marker
     enabled frame_sign_bias && enable_feature frame_marker
     enabled txmg && enable_feature highbitdepth
     enabled ext_skip && enable_feature frame_marker