Add a TODO

Change-Id: I16bf93d40e9b345705b49bf09dd4b6996b513a83

vp9/encoder/vp9_tokenize.c

@@ -288,7 +288,6 @@ struct is_skippable_args {
   MACROBLOCK *x;
   int *skippable;
 };
-
 static void is_skippable(int plane, int block,
                          BLOCK_SIZE plane_bsize, TX_SIZE tx_size,
                          void *argv) {
@@ -298,6 +297,8 @@ static void is_skippable(int plane, int block,
   args->skippable[0] &= (!args->x->plane[plane].eobs[block]);
 }
 
+// TODO(yaowu): rewrite and optimize this function to remove the usage of
+//              vp9_foreach_transform_block() and simplify is_skippable().
 int vp9_is_skippable_in_plane(MACROBLOCK *x, BLOCK_SIZE bsize, int plane) {
   int result = 1;
   struct is_skippable_args args = {x, &result};