Remove the dependency of TransportChannel and TransportChannelImpl.

webrtc/p2p/base/dtlstransportinternal.h

Index: webrtc/p2p/base/dtlstransportinternal.h
diff --git a/webrtc/p2p/base/dtlstransportinternal.h b/webrtc/p2p/base/dtlstransportinternal.h
index 780c128e0068fbc2b7c3ceb48a395bc268c054dc..74fdd6dfcfd9403bc431006bfbe178566833bb4f 100644
--- a/webrtc/p2p/base/dtlstransportinternal.h
+++ b/webrtc/p2p/base/dtlstransportinternal.h
@@ -22,6 +22,12 @@
 
 namespace cricket {
 
+enum PacketFlags {
+  PF_NORMAL = 0x00,       // A normal packet.
+  PF_SRTP_BYPASS = 0x01,  // An encrypted SRTP packet; bypass any additional
+                          // crypto provided by the transport (e.g. DTLS)
+};
+
 // DtlsTransportInternal is an internal interface that does DTLS.
 // Once the public interface is supported,
 // (https://www.w3.org/TR/webrtc/#rtcdtlstransport-interface)
@@ -94,6 +100,9 @@ class DtlsTransportInternal : public rtc::PacketTransportInterface {
     return transport_name() + " " + std::to_string(component());
   }
 
+ protected:
+  DtlsTransportInternal() {}
+
  private:
   RTC_DISALLOW_COPY_AND_ASSIGN(DtlsTransportInternal);
 };