Add ffmpegsumo.dll to 'symsrc' group for symbol upload.

BUG=164036
TEST=none
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/11434093

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@170830 0039d316-1c4b-4281-b951-d872f2087c98

chrome/tools/build/win/FILES.cfg

@@ -40,6 +40,7 @@ FILES = [
     'filename': 'ffmpegsumo.dll',
     'arch': ['32bit', '64bit'],
     'buildtype': ['dev', 'official'],
+    'filegroup': ['default', 'symsrc'],
   },
   {
     'filename': 'chrome.exe',