Add support for GCM cipher suites from RFC 7714.

webrtc/p2p/base/transportchannel.h

Index: webrtc/p2p/base/transportchannel.h
diff --git a/webrtc/p2p/base/transportchannel.h b/webrtc/p2p/base/transportchannel.h
index b91af139b7155d35589305deef52cb0bb7308eb5..1e38405b67bc48d629c26ff34b469b293b663af9 100644
--- a/webrtc/p2p/base/transportchannel.h
+++ b/webrtc/p2p/base/transportchannel.h
@@ -124,6 +124,9 @@ class TransportChannel : public sigslot::has_slots<> {
   // TODO(guoweis): Remove this once all dependencies implement this.
   virtual bool GetSslCipherSuite(int* cipher) { return false; }
 
+  // May GCM ciphers be used?
+  virtual bool IsEnableGcmCiphers() const { return false; }
+
   // Gets the local RTCCertificate used for DTLS.
   virtual rtc::scoped_refptr<rtc::RTCCertificate>
   GetLocalCertificate() const = 0;