Allow HttpDecoder to report metadata of SETTINGS frame to visitor.

gfe-relnote: new API, not used.
PiperOrigin-RevId: 241572090
Change-Id: Ibc83a3e99727317ba95f62060338a279195c5d89
diff --git a/quic/core/http/http_decoder.h b/quic/core/http/http_decoder.h
index 1cc973a..2318a03 100644
--- a/quic/core/http/http_decoder.h
+++ b/quic/core/http/http_decoder.h
@@ -56,6 +56,9 @@
     // Called when a GOAWAY frame has been successfully parsed.
     virtual void OnGoAwayFrame(const GoAwayFrame& frame) = 0;
 
+    // Called when a SETTINGS frame has been received.
+    virtual void OnSettingsFrameStart(Http3FrameLengths frame_length) = 0;
+
     // Called when a SETTINGS frame has been successfully parsed.
     virtual void OnSettingsFrame(const SettingsFrame& frame) = 0;