Give VP9 a different sync code from VP8

The new code is 0x49, 0x83, 0x42

There is nothing particularly special about this code bitstream wise.
Its derivation is the word "sync" coded using 4x6bit alphabetic indices.

Change-Id: Ie2430a854af32ddc5a5c25a6c1c90cf6497ba647

vp9/decoder/vp9_decodframe.c

@@ -959,7 +959,7 @@ int vp9_decode_frame(VP9D_COMP *pbi, const uint8_t **p_data_end) {
       // When error concealment is enabled we should only check the sync
       // code if we have enough bits available
       if (data + 3 < data_end) {
-        if (data[0] != 0x9d || data[1] != 0x01 || data[2] != 0x2a)
+        if (data[0] != 0x49 || data[1] != 0x83 || data[2] != 0x42)
           vpx_internal_error(&pc->error, VPX_CODEC_UNSUP_BITSTREAM,
                              "Invalid frame sync code");
       }

vp9/encoder/vp9_bitstream.c

@@ -1506,9 +1506,9 @@ void vp9_pack_bitstream(VP9_COMP *cpi, uint8_t *dest, unsigned long *size) {
    */
   if (oh.type == KEY_FRAME) {
     // Start / synch code
-    cx_data[0] = 0x9D;
-    cx_data[1] = 0x01;
-    cx_data[2] = 0x2a;
+    cx_data[0] = 0x49;
+    cx_data[1] = 0x83;
+    cx_data[2] = 0x42;
     extra_bytes_packed = 3;
     cx_data += extra_bytes_packed;
   }

vp9/vp9_dx_iface.c

@@ -217,7 +217,7 @@ static vpx_codec_err_t vp8_peek_si(const uint8_t         *data,
   else {
     /* Parse uncompresssed part of key frame header.
      * 3 bytes:- including version, frame type and an offset
-     * 3 bytes:- sync code (0x9d, 0x01, 0x2a)
+     * 3 bytes:- sync code (0x49, 0x83, 0x42)
      * 4 bytes:- including image width and height in the lowest 14 bits
      *           of each 2-byte value.
      */
@@ -228,7 +228,7 @@ static vpx_codec_err_t vp8_peek_si(const uint8_t         *data,
       si->is_kf = 1;
 
       /* vet via sync code */
-      if (c[0] != 0x9d || c[1] != 0x01 || c[2] != 0x2a)
+      if (c[0] != 0x49 || c[1] != 0x83 || c[2] != 0x42)
         res = VPX_CODEC_UNSUP_BITSTREAM;
 
       si->w = (c[3] | (c[4] << 8));