Add support for GCM cipher suites from RFC 7714.

webrtc/p2p/base/dtlstransportchannel.cc

Index: webrtc/p2p/base/dtlstransportchannel.cc
diff --git a/webrtc/p2p/base/dtlstransportchannel.cc b/webrtc/p2p/base/dtlstransportchannel.cc
index 95014f9a6250c534e3e08b8a8882384e308dd17e..6695da406ab152c0242864e185f8b5c9abc28fe8 100644
--- a/webrtc/p2p/base/dtlstransportchannel.cc
+++ b/webrtc/p2p/base/dtlstransportchannel.cc
@@ -95,7 +95,8 @@ DtlsTransportChannelWrapper::DtlsTransportChannelWrapper(
       channel_(channel),
       downward_(NULL),
       ssl_role_(rtc::SSL_CLIENT),
-      ssl_max_version_(rtc::SSL_PROTOCOL_DTLS_10) {
+      ssl_max_version_(rtc::SSL_PROTOCOL_DTLS_10),
+      enable_gcm_ciphers_(false) {
   channel_->SignalWritableState.connect(this,
       &DtlsTransportChannelWrapper::OnWritableState);
   channel_->SignalReadPacket.connect(this,
@@ -167,6 +168,21 @@ bool DtlsTransportChannelWrapper::SetSslMaxProtocolVersion(
   return true;
 }
 
+bool DtlsTransportChannelWrapper::SetEnableGcmCiphers(bool enable) {
+  if (dtls_active_) {
+    LOG(LS_ERROR) << "Not changing enabled GCM ciphers "
+                  << "while DTLS is negotiating";
+    return false;
+  }
+
+  enable_gcm_ciphers_ = enable;
+  return true;
+}
+
+bool DtlsTransportChannelWrapper::IsEnableGcmCiphers() const {
+  return enable_gcm_ciphers_;
+}
+
 bool DtlsTransportChannelWrapper::SetSslRole(rtc::SSLRole role) {
   if (dtls_state() == DTLS_TRANSPORT_CONNECTED) {
     if (ssl_role_ != role) {