Fix partition type costing.

This patch makes rd optimization use the same context for computing
the rate cost of coding the partitioning as the packer actually uses
when emitting it in write_modes_sb.

Change-Id: Idb1427bb2f9c37ab80c6aa182f7ff754ef0595cb

vp10/encoder/encodeframe.c

diff --git a/vp10/encoder/encodeframe.c b/vp10/encoder/encodeframe.c
index 859ec49..e26505f 100644
--- a/vp10/encoder/encodeframe.c
+++ b/vp10/encoder/encodeframe.c
@@ -2875,7 +2875,8 @@
 #endif
   TOKENEXTRA *tp_orig = *tp;
   PICK_MODE_CONTEXT *ctx = &pc_tree->none;
-  int i, pl;
+  int i;
+  const int pl = partition_plane_context(xd, mi_row, mi_col, bsize);
   BLOCK_SIZE subsize;
   RD_COST this_rdc, sum_rdc, best_rdc;
 #if CONFIG_SUPERTX
@@ -3021,7 +3022,6 @@
                      bsize, ctx, best_rdc.rdcost);
     if (this_rdc.rate != INT_MAX) {
       if (bsize >= BLOCK_8X8) {
-        pl = partition_plane_context(xd, mi_row, mi_col, bsize);
         this_rdc.rate += cpi->partition_cost[pl][PARTITION_NONE];
         this_rdc.rdcost = RDCOST(x->rdmult, x->rddiv,
                                  this_rdc.rate, this_rdc.dist);
@@ -3288,7 +3288,6 @@
     }
 
     if (sum_rdc.rdcost < best_rdc.rdcost && i == 4) {
-      pl = partition_plane_context(xd, mi_row, mi_col, bsize);
       sum_rdc.rate += cpi->partition_cost[pl][PARTITION_SPLIT];
       sum_rdc.rdcost = RDCOST(x->rdmult, x->rddiv,
                               sum_rdc.rate, sum_rdc.dist);
@@ -3427,7 +3426,6 @@
 #endif  // CONFIG_SUPERTX
 
     if (sum_rdc.rdcost < best_rdc.rdcost) {
-      pl = partition_plane_context(xd, mi_row, mi_col, bsize);
       sum_rdc.rate += cpi->partition_cost[pl][PARTITION_HORZ];
       sum_rdc.rdcost = RDCOST(x->rdmult, x->rddiv, sum_rdc.rate, sum_rdc.dist);
 #if CONFIG_SUPERTX
@@ -3556,7 +3554,6 @@
 #endif  // CONFIG_SUPERTX
 
     if (sum_rdc.rdcost < best_rdc.rdcost) {
-      pl = partition_plane_context(xd, mi_row, mi_col, bsize);
       sum_rdc.rate += cpi->partition_cost[pl][PARTITION_VERT];
       sum_rdc.rdcost = RDCOST(x->rdmult, x->rddiv,
                               sum_rdc.rate, sum_rdc.dist);