[Cast Channel] Add support for nonce challenge to Cast channel authentication.

extensions/browser/api/cast_channel/cast_socket.h

Index: extensions/browser/api/cast_channel/cast_socket.h
diff --git a/extensions/browser/api/cast_channel/cast_socket.h b/extensions/browser/api/cast_channel/cast_socket.h
index 2fa1821d7ca054fa369b02f37c06ae6c7036707f..94c08b1b895ec59e38e49fe1e82c953394101297 100644
--- a/extensions/browser/api/cast_channel/cast_socket.h
+++ b/extensions/browser/api/cast_channel/cast_socket.h
@@ -145,6 +145,7 @@ class CastSocketImpl : public CastSocket {
   // |net_log|: Log of socket events.
   // |connect_timeout|: Connection timeout interval.
   // |logger|: Log of cast channel events.
+  // |nonce|: The nonce challenge.
   CastSocketImpl(const std::string& owner_extension_id,
                  const net::IPEndPoint& ip_endpoint,
                  ChannelAuthType channel_auth,
@@ -152,7 +153,8 @@ class CastSocketImpl : public CastSocket {
                  const base::TimeDelta& connect_timeout,
                  bool keep_alive,
                  const scoped_refptr<Logger>& logger,
-                 uint64_t device_capabilities);
+                 uint64_t device_capabilities,
+                 const std::string& nonce);
 
   // Ensures that the socket is closed.
   ~CastSocketImpl() override;
@@ -379,6 +381,9 @@ class CastSocketImpl : public CastSocket {
   // information.
   AuthTransportDelegate* auth_delegate_;
 
+  // The nonce challenge to send to the Cast receiver.
+  std::string nonce_;
+
   DISALLOW_COPY_AND_ASSIGN(CastSocketImpl);
 };
 }  // namespace cast_channel