More TSan v2 suppressions for content_browsertests:
 - races on a vector in cricket::P2PTransportChannel (issue 348982)
 - races in usrsctp (issue 348984)

BUG=348982,348984
TBR=timurrrr@chromium.org

Review URL: https://codereview.chromium.org/186633003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254757 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254757