GN: Add peerconnection_unittests

BUG=webrtc:5949
TESTED=Built and ran the tests on Mac.
NOTRY=True

Review-Url: https://codereview.webrtc.org/2054413002
Cr-Original-Commit-Position: refs/heads/master@{#13116}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: fd5b4e9435b2b3f7069ecfda02ec40931c4b642b
2 files changed