Add support for GCM cipher suites from RFC 7714.

webrtc/pc/srtpfilter.h

Index: webrtc/pc/srtpfilter.h
diff --git a/webrtc/pc/srtpfilter.h b/webrtc/pc/srtpfilter.h
index cde9ad7e09c84dbc4a0214cba3505768c3bfcf5b..0b7dcf3e70e99a78eac75e3d8dbbaebce5a7aaa6 100644
--- a/webrtc/pc/srtpfilter.h
+++ b/webrtc/pc/srtpfilter.h
@@ -33,13 +33,6 @@ struct srtp_policy_t;
 
 namespace cricket {
 
-// Key is 128 bits and salt is 112 bits == 30 bytes. B64 bloat => 40 bytes.
-extern const int SRTP_MASTER_KEY_BASE64_LEN;
-
-// Needed for DTLS-SRTP
-extern const int SRTP_MASTER_KEY_KEY_LEN;
-extern const int SRTP_MASTER_KEY_SALT_LEN;
-
 class SrtpSession;
 class SrtpStat;