This patch fixes the compatibility for loop-count handling.
This aims at addressing the change in Chrome handling of loop-count
prior to M63.
Before M63: loop-count interpretation was aligned to GIF's behaviour in
Chrome, but incompatible with WebP's spec. In particular, you couldn't
loop exactly once.
Post-M63: loop-count in WebP is really the total number of loops. Gif2webp
will convert correctly from a GIF source by adjusting the loop count.
Note: The Chrome version can be retrieved from the User-Agent
string (chrome://version).
An M63 version will contain the pattern:
Chrome/63.x.xxxx.xx
for instance.
Change-Id: Ie6dc13227e6498f4d7af2f09247913648997648a
b4e046778d