Roll src/third_party/ffmpeg/ 18c815f81..23e0b491f (1 commit)

https://chromium.googlesource.com/chromium/third_party/ffmpeg.git/+log/18c815f81428..23e0b491fa58

$ git log 18c815f81..23e0b491f --date=short --no-merges --format='%ad %ae %s'
2017-11-30 dalecurtis Fix another 1 << 31 > int32_t::max() with 1u.

Created with:
  roll-dep src/third_party/ffmpeg

BUG=788343
TEST=no more ubsan issue.
TBR=sandersd

Change-Id: I3511f4b657a56251812fec25a4c792578598e676
Reviewed-on: https://chromium-review.googlesource.com/801352Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520703}

DEPS

@@ -330,7 +330,7 @@ deps = {
   },
 
   'src/third_party/ffmpeg':
-    Var('chromium_git') + '/chromium/third_party/ffmpeg.git' + '@' + '18c815f81428e3b41e6f4efc6cb0cbe5b846d1c2',
+    Var('chromium_git') + '/chromium/third_party/ffmpeg.git' + '@' + '23e0b491fa58a44cf9b2b386a29c69e67169ef19',
 
   'src/third_party/findbugs': {
       'url': Var('chromium_git') + '/chromium/deps/findbugs.git' + '@' + '4275d9ac8610db6b1bc9a5e887f97e41b33fac67',