Add async variant of ProofSource::GetProof

net/quic/crypto/proof_source_chromium.h

Index: net/quic/crypto/proof_source_chromium.h
diff --git a/net/quic/crypto/proof_source_chromium.h b/net/quic/crypto/proof_source_chromium.h
index f84746ee0cf48b64b22b61a209f95832b1f74a95..904bd0dd7d8ff0271d560e4579fa0cfccef927c8 100644
--- a/net/quic/crypto/proof_source_chromium.h
+++ b/net/quic/crypto/proof_source_chromium.h
@@ -43,6 +43,14 @@ class NET_EXPORT_PRIVATE ProofSourceChromium : public ProofSource {
                 std::string* out_signature,
                 std::string* out_leaf_cert_sct) override;
 
+  void GetProof(const IPAddress& server_ip,
+                const std::string& hostname,
+                const std::string& server_config,
+                QuicVersion quic_version,
+                base::StringPiece chlo_hash,
+                bool ecdsa_ok,
+                std::unique_ptr<Callback> callback) override;
+
  private:
   std::unique_ptr<crypto::RSAPrivateKey> private_key_;
   scoped_refptr<ProofSource::Chain> chain_;