Roll ffmpeg DEPs for security fixes. Add regression tests.

DEPS

 # This file is used to manage the dependencies of the Chromium src repo. It is
 # used by gclient to determine what version of each dependency to check out, and
 # where.
 #
 # For more information, please refer to the official documentation:
 #   https://sites.google.com/a/chromium.org/dev/developers/how-tos/get-the-code
 #
 # When adding a new dependency, please update the top-level .gitignore file
 # to list the dependency's destination directory.
 #
@@ skipping 199 matching lines @@
   'src/third_party/swig/Lib':
    Var('chromium_git') + '/chromium/deps/swig/Lib.git' + '@' + 'f2a695d52e61e6a8d967731434f165ed400f0d69',
 
   'src/third_party/webdriver/pylib':
     Var('chromium_git') + '/external/selenium/py.git' + '@' + '5fd78261a75fe08d27ca4835fb6c5ce4b42275bd',
 
   'src/third_party/libvpx':
    Var('chromium_git') + '/chromium/deps/libvpx.git' + '@' +  Var('libvpx_revision'),
 
   'src/third_party/ffmpeg':
-   Var('chromium_git') + '/chromium/third_party/ffmpeg.git' + '@' + 'b5bc821a0a85808e445cb82156c6714d5288b4e3',
+   Var('chromium_git') + '/chromium/third_party/ffmpeg.git' + '@' + 'b9d631d0ad277109678e86d729acc889793b4b94',
 
   'src/third_party/libjingle/source/talk':
     Var('chromium_git') + '/external/webrtc/trunk/talk.git' + '@' + '1aaae712f168d0a023c20c936867a766a4f65674', # from svn revision 7972
 
   'src/third_party/usrsctp/usrsctplib':
     Var('chromium_git') + '/external/usrsctplib.git' + '@' + '190c8cbfcf8fd810aa09e0fab4ca62a8ce724e14',
 
   'src/third_party/libsrtp':
    Var('chromium_git') + '/chromium/deps/libsrtp.git' + '@' + '6446144c7f083552f21cc4e6768e891bcb767574',
 
@@ skipping 563 matching lines @@
     # corresponding .py files have already been deleted.
     'name': 'remove_stale_pyc_files',
     'pattern': 'src/tools/.*\\.py',
     'action': [
         'python',
         'src/tools/remove_stale_pyc_files.py',
         'src/tools',
     ],
   },
 ]