Fix memory leak in FakeSSLCertificate::GetChain(), discovered by Linux Memcheck build/try bots.

TBR=hellner
BUG=

Review URL: https://webrtc-codereview.appspot.com/18969004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6809 4adac7df-926f-26a2-2b94-8c16560cd09d