gfe-relnote: Print out a SPDY_BUG and exit early rather than crash when Http2FrameDecoderAdapter is nullptr.  Not flag protected.

PiperOrigin-RevId: 257106748
Change-Id: I587ccf7a4adc43a2f61c5cf75994e1c56ec3c715

spdy/core/http2_frame_decoder_adapter.cc

diff --git a/spdy/core/http2_frame_decoder_adapter.cc b/spdy/core/http2_frame_decoder_adapter.cc
index 84e083f..ac53496 100644
--- a/spdy/core/http2_frame_decoder_adapter.cc
+++ b/spdy/core/http2_frame_decoder_adapter.cc
@@ -398,6 +398,11 @@
   DCHECK(!on_headers_called_);
   on_headers_called_ = true;
   ReportReceiveCompressedFrame(frame_header_);
+  if (!visitor()) {
+    SPDY_BUG << "Visitor is nullptr, handling priority in headers failed."
+             << " priority:" << priority << " frame_header:" << frame_header_;
+    return;
+  }
   visitor()->OnHeaders(frame_header_.stream_id, kHasPriorityFields,
                        priority.weight, priority.stream_dependency,
                        priority.is_exclusive, frame_header_.IsEndStream(),