Fix some spurious warnings for third party libs.

These warnings are non actionable because they appear in third_party
code, silence them.
BUG=341086
TBR=brettw

Review URL: https://codereview.chromium.org/156953002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252497 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252497