Add flag FRAME_COUNTER_FOR_SCALABILITY

This flag is to guard the implementation in the codebase, to address
the adopted proposal as follows:

Frame Counter Update For Scalable Structures
(frame_counter_for_scalability)

Once the implementation is completed and tested, the flag will be
removed.

BUG=aomedia:1425

Change-Id: I7e273110b0db48954b8f646685c1cb4570773c36

build/cmake/aom_config_defaults.cmake

diff --git a/build/cmake/aom_config_defaults.cmake b/build/cmake/aom_config_defaults.cmake
index 792941d..ba3eed1 100644
--- a/build/cmake/aom_config_defaults.cmake
+++ b/build/cmake/aom_config_defaults.cmake
@@ -102,6 +102,7 @@
 set(CONFIG_FILM_GRAIN 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_FILM_GRAIN_SHOWEX 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_FP_MB_STATS 0 CACHE NUMBER "AV1 experiment flag.")
+set(CONFIG_FRAME_COUNTER_FOR_SCALABILITY 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_FRAME_REFS_SIGNALING 0 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.")

build/cmake/aom_experiment_deps.cmake

diff --git a/build/cmake/aom_experiment_deps.cmake b/build/cmake/aom_experiment_deps.cmake
index cea748a..de7ae1b 100644
--- a/build/cmake/aom_experiment_deps.cmake
+++ b/build/cmake/aom_experiment_deps.cmake
@@ -50,6 +50,13 @@
       change_config_and_warn(CONFIG_RD_DEBUG 0 CONFIG_JNT_COMP)
     endif()
   endif()
+
+  if (CONFIG_FRAME_COUNTER_FOR_SCALABILITY)
+    if (NOT CONFIG_SCALABILITY)
+      change_config_and_warn(CONFIG_SCALABILITY 1
+                             CONFIG_FRAME_COUNTER_FOR_SCALABILITY)
+    endif ()
+  endif()
 endmacro ()
 
 endif ()  # AOM_BUILD_CMAKE_AOM_EXPERIMENT_DEPS_CMAKE_