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 523ac1dcbfe2a7c1eec377c22af13c6c4fff6e09..a0c3f601aea7f368fcc5073c28c572ccca5b56d5 100644
--- a/webrtc/pc/srtpfilter.h
+++ b/webrtc/pc/srtpfilter.h
@@ -32,13 +32,6 @@ 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;