Upload pdf.dll symbols to chromium symbol server.

BUG=405223

Review URL: https://codereview.chromium.org/489593005

Cr-Commit-Position: refs/heads/master@{#290690}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@290690 0039d316-1c4b-4281-b951-d872f2087c98

chrome/tools/build/win/FILES.cfg

@@ -353,6 +353,7 @@ FILES = [
   {
     'filename': 'pdf.dll',
     'buildtype': ['dev', 'official'],
+    'filegroup': ['default', 'symsrc'],
   },
   # ANGLE files:
   {