Add support for GCM cipher suites from RFC 7714.

webrtc/p2p/base/dtlstransportchannel.h

Index: webrtc/p2p/base/dtlstransportchannel.h
diff --git a/webrtc/p2p/base/dtlstransportchannel.h b/webrtc/p2p/base/dtlstransportchannel.h
index 955b963a3657a1efc7436e4347158b02e7e112e2..869dc0e399dd51e96413f6311594451fbe076a4b 100644
--- a/webrtc/p2p/base/dtlstransportchannel.h
+++ b/webrtc/p2p/base/dtlstransportchannel.h
@@ -123,6 +123,10 @@ class DtlsTransportChannelWrapper : public TransportChannelImpl {
 
   virtual bool SetSslMaxProtocolVersion(rtc::SSLProtocolVersion version);
 
+  virtual bool SetEnableGcmCiphers(bool enable);
+
+  bool IsEnableGcmCiphers() const override;
+
   // Set up the ciphers to use for DTLS-SRTP. If this method is not called
   // before DTLS starts, or |ciphers| is empty, SRTP keys won't be negotiated.
   // This method should be called before SetupDtls.
@@ -229,6 +233,7 @@ class DtlsTransportChannelWrapper : public TransportChannelImpl {
   rtc::scoped_refptr<rtc::RTCCertificate> local_certificate_;
   rtc::SSLRole ssl_role_;
   rtc::SSLProtocolVersion ssl_max_version_;
+  bool enable_gcm_ciphers_;
   rtc::Buffer remote_fingerprint_value_;
   std::string remote_fingerprint_algorithm_;