tree 1d06bd5de8bd17d64df5d75d8f9dc99ae0666c1f
parent 28af7875cc8fa9a3091bdef039c00b748b353fc4
author Wan-Teh Chang <wtc@google.com> 1600305720 -0700
committer Wan-Teh Chang <wtc@google.com> 1601319553 +0000

Document the has_val field of the arg_def_t struct

Until commit 4c2b30effc114f32e98a93d5fdb6ce02d19da04d
(https://aomedia-review.googlesource.com/c/aom/+/116721), the has_val
field of the arg_def_t struct had been used as a regular boolean, with
values 0 and 1. The special value of -1 was introduced in that commit to
indicate that the command-line argument has an optional value.

Add a comment to document the three possible values (0, 1, and -1).

Change-Id: Ide9cfe8e8bd377400392c88b52d289d4d6a1d6e2