Improve LEB128 support and test coverage.

Also some minor cosmetic changes and style fixes.

BUG=aomedia:1125

Change-Id: Ide24057736376accd2f9907ef87b5a725ab3f3c2
diff --git a/av1/encoder/bitstream.c b/av1/encoder/bitstream.c
index b78e95c..c12016d 100644
--- a/av1/encoder/bitstream.c
+++ b/av1/encoder/bitstream.c
@@ -4574,7 +4574,7 @@
 int write_uleb_obu_size(uint32_t obu_size, uint8_t *dest) {
   size_t coded_obu_size = 0;
 
-  if (aom_uleb_encode(obu_size, sizeof(uint32_t), dest, &coded_obu_size) != 0)
+  if (aom_uleb_encode(obu_size, sizeof(obu_size), dest, &coded_obu_size) != 0)
     return AOM_CODEC_ERROR;
 
   return AOM_CODEC_OK;