Adds a missing include for std::unique_ptr.

PiperOrigin-RevId: 399477224

http2/adapter/nghttp2_data_provider.h

diff --git a/http2/adapter/nghttp2_data_provider.h b/http2/adapter/nghttp2_data_provider.h
index 680564b..9e9119f 100644
--- a/http2/adapter/nghttp2_data_provider.h
+++ b/http2/adapter/nghttp2_data_provider.h
@@ -2,6 +2,7 @@
 #define QUICHE_HTTP2_ADAPTER_NGHTTP2_DATA_PROVIDER_H_
 
 #include <cstdint>
+#include <memory>
 
 #include "http2/adapter/data_source.h"
 #include "third_party/nghttp2/src/lib/includes/nghttp2/nghttp2.h"