Roll src/third_party/ffmpeg/ 4b75b8bab..41268576a (2 commits)

https://chromium.googlesource.com/chromium/third_party/ffmpeg.git/+log/4b75b8bab993..41268576ad9a

$ git log 4b75b8bab..41268576a --date=short --no-merges --format='%ad %ae %s'
2019-02-08 chcunningham avformat/mov.c: require tfhd to begin parsing trun
2019-02-08 chcunningham avformat/mov: validate chunk_count vs stsc_data

Created with:
  roll-dep src/third_party/ffmpeg

Bug: 906384, 919573
TBR: dalecurtis@chromium.org
Change-Id: Iaeefcddc5324bb48b3c74a0ebaae20a794266f1b
Reviewed-on: https://chromium-review.googlesource.com/c/1461682Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Commit-Queue: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630604}

DEPS

@@ -789,7 +789,7 @@ deps = {
   },
 
   'src/third_party/ffmpeg':
-    Var('chromium_git') + '/chromium/third_party/ffmpeg.git' + '@' + '4b75b8bab99385646911c24403a016ce9c3d5740',
+    Var('chromium_git') + '/chromium/third_party/ffmpeg.git' + '@' + '41268576ad9a8b760287101f4f58d0ef468798af',
 
   'src/third_party/flac':
     Var('chromium_git') + '/chromium/deps/flac.git' + '@' + 'af862024c8c8fa0ae07ced05e89013d881b00596',