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

extensions/browser/api/cast_channel/cast_socket_unittest.cc

Index: extensions/browser/api/cast_channel/cast_socket_unittest.cc
diff --git a/extensions/browser/api/cast_channel/cast_socket_unittest.cc b/extensions/browser/api/cast_channel/cast_socket_unittest.cc
index 48e60c83a6bcac8103a807fdfb9c3ab073fb5bb8..fb57ef582c3ce8f5b4dbfe3e5ccf4b657973e855 100644
--- a/extensions/browser/api/cast_channel/cast_socket_unittest.cc
+++ b/extensions/browser/api/cast_channel/cast_socket_unittest.cc
@@ -60,7 +60,7 @@ const char kAuthNamespace[] = "urn:x-cast:com.google.cast.tp.deviceauth";
 // Returns an auth challenge message inline.
 CastMessage CreateAuthChallenge() {
   CastMessage output;
-  CreateAuthChallengeMessage(&output);
+  CreateAuthChallengeMessage(&output, "");
   return output;
 }
 
@@ -215,7 +215,9 @@ class TestCastSocket : public CastSocketImpl {
         verify_challenge_disallow_(false),
         tcp_unresponsive_(false),
         mock_timer_(new base::MockTimer(false, false)),
-        mock_transport_(nullptr) {}
+        mock_transport_(nullptr) {
+    nonce_ = "";
+  }
 
   ~TestCastSocket() override {}