Add support of serving SCT on the server side in QUIC, gated by QUIC_VERSION_30.

net/quic/test_tools/crypto_test_utils_chromium.cc

Index: net/quic/test_tools/crypto_test_utils_chromium.cc
diff --git a/net/quic/test_tools/crypto_test_utils_chromium.cc b/net/quic/test_tools/crypto_test_utils_chromium.cc
index ffa1788c0148daa6acbf26631566b825765011dc..73bf96a817b3685aceeccc9a5290156e71216366 100644
--- a/net/quic/test_tools/crypto_test_utils_chromium.cc
+++ b/net/quic/test_tools/crypto_test_utils_chromium.cc
@@ -65,7 +65,8 @@ class FakeProofSource : public ProofSource {
                 const std::string& server_config,
                 bool ecdsa_ok,
                 const std::vector<std::string>** out_certs,
-                std::string* out_signature) override {
+                std::string* out_signature,
+                std::string* out_leaf_cert_sct) override {
     *out_certs = &certs_;
     *out_signature = kSignature;
     return true;