Add HttpDecoder::OnPriorityFrameStart() so that QuicSpdyStream knows the size
of the priority frame and can consume correct amount of bytes.

gfe-relnote: v99 only, not in prod.
PiperOrigin-RevId: 254279623
Change-Id: Ic24fd04b055033c0735a224e76a949714b3ef268
diff --git a/quic/core/http/http_decoder.h b/quic/core/http/http_decoder.h
index 9f0db73..0304b56 100644
--- a/quic/core/http/http_decoder.h
+++ b/quic/core/http/http_decoder.h
@@ -40,6 +40,11 @@
     // Called if an error is detected.
     virtual void OnError(HttpDecoder* decoder) = 0;
 
+    // Called when a PRIORITY frame has been received.
+    // |frame_length| contains PRIORITY frame length and payload length.
+    // Returns true to permit furthuring decoding, and false to prevent it.
+    virtual bool OnPriorityFrameStart(Http3FrameLengths frame_length) = 0;
+
     // Called when a PRIORITY frame has been successfully parsed.
     // Returns true to permit furthuring decoding, and false to prevent it.
     virtual bool OnPriorityFrame(const PriorityFrame& frame) = 0;