http2: track nghttp2-allocated memory in heap snapshot

PR-URL: #30745
Refs: https://github.com/nodejs/quic/blob/34ee0bc96f804c73cb22b2945a1a78f780938492/src/node_mem.h
Refs: nodejs/quic#126
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: addaleax

src/node_http2.h

@@ -794,6 +794,7 @@ class Http2Session : public AsyncWrap,
     tracker->TrackFieldWithSize("outgoing_storage", outgoing_storage_.size());
     tracker->TrackFieldWithSize("pending_rst_streams",
                                 pending_rst_streams_.size() * sizeof(int32_t));
+    tracker->TrackFieldWithSize("nghttp2_memory", current_nghttp2_memory_);
   }
 
   SET_MEMORY_INFO_NAME(Http2Session)

test/pummel/test-heapdump-http2.js

@@ -69,6 +69,7 @@ server.listen(0, () => {
       {
         children: [
           { node_name: 'Http2Session', edge_name: 'wrapped' },
+          { node_name: 'Node / nghttp2_memory', edge_name: 'nghttp2_memory' },
           {
             node_name: 'Node / streams', edge_name: 'streams'
           }