Make OBU_SIZING work with EXT_TILE

In OBU_SIZING, length_field_size is determined adaptively after an OBU
unit is encoded. The positions to write tile_col_size and tile_size
need to be adjusted accordingly after frame header is re-positioned.
This patch fixed the issue and re-enabled LEB128 OBU size fields.

BUG=aomedia:1439

Change-Id: Ia090d3482048411f34f0c9c687b7f92fb34262dc

av1/encoder/bitstream.c

diff --git a/av1/encoder/bitstream.c b/av1/encoder/bitstream.c
index 5aae9f7..27e3a66 100644
--- a/av1/encoder/bitstream.c
+++ b/av1/encoder/bitstream.c
@@ -4112,6 +4112,11 @@
 #endif  // CONFIG_OBU_SIZING
 
   data += obu_size + length_field_size;
+#if CONFIG_EXT_TILE
+  // Since length_field_size is determined adaptively after frame header
+  // encoding, saved_wb must be adjusted accordingly.
+  saved_wb.bit_buffer += length_field_size;
+#endif
 
   if (cm->show_existing_frame) {
     data_size = 0;

build/cmake/aom_config_defaults.cmake

diff --git a/build/cmake/aom_config_defaults.cmake b/build/cmake/aom_config_defaults.cmake
index 4a0fd49..0625ce4 100644
--- a/build/cmake/aom_config_defaults.cmake
+++ b/build/cmake/aom_config_defaults.cmake
@@ -126,7 +126,7 @@
 set(CONFIG_MONO_VIDEO 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_NO_FRAME_CONTEXT_SIGNALING 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_OBU_NO_IVF 0 CACHE NUMBER "AV1 experiment flag.")
-set(CONFIG_OBU_SIZING 0 CACHE NUMBER "AV1 experiment flag.")
+set(CONFIG_OBU_SIZING 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_OPT_REF_MV 1 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_RD_DEBUG 0 CACHE NUMBER "AV1 experiment flag.")
 set(CONFIG_SCALABILITY 1 CACHE NUMBER "AV1 experiment flag.")