Make RTC coding flow support sub8x8 in key frame coding

This commit enables the use of sub8x8 blocks in RTC key frame
encoding. It requires the block size to be preset and will decide
the coding mode and encode the bit-stream.

Change-Id: I35aaf8ee2d4d6085432410c7963f339f85a2c19b

vp9/encoder/vp9_encodeframe.c

@@ -3247,6 +3247,12 @@ static void nonrd_use_partition(VP9_COMP *cpi,
       break;
     case PARTITION_SPLIT:
       subsize = get_subsize(bsize, PARTITION_SPLIT);
+      if (bsize == BLOCK_8X8) {
+        nonrd_pick_sb_modes(cpi, tile_data, x, mi_row, mi_col, dummy_cost,
+                            subsize, pc_tree->leaf_split[0]);
+        encode_b_rt(cpi, td, tile_info, tp, mi_row, mi_col,
+                    output_enabled, subsize, pc_tree->leaf_split[0]);
+      } else {
         nonrd_use_partition(cpi, td, tile_data, mi, tp, mi_row, mi_col,
                             subsize, output_enabled, dummy_cost,
                             pc_tree->split[0]);
@@ -3259,6 +3265,7 @@ static void nonrd_use_partition(VP9_COMP *cpi,
         nonrd_use_partition(cpi, td, tile_data, mi + hbs * mis + hbs, tp,
                             mi_row + hbs, mi_col + hbs, subsize, output_enabled,
                             dummy_cost, pc_tree->split[3]);
+      }
       break;
     default:
       assert(0 && "Invalid partition type.");
@@ -3299,6 +3306,9 @@ static void encode_nonrd_sb_row(VP9_COMP *cpi,
     // Set the partition type of the 64X64 block
     switch (sf->partition_search_type) {
       case VAR_BASED_PARTITION:
+        // TODO(jingning) Only key frame coding supports sub8x8 block at this
+        // point. To be continued to enable sub8x8 block mode decision for
+        // P frames.
         choose_partitioning(cpi, tile_info, x, mi_row, mi_col);
         nonrd_use_partition(cpi, td, tile_data, mi, tp, mi_row, mi_col,
                             BLOCK_64X64, 1, &dummy_rdc, td->pc_root);