Clean up QuicSpdySession destructor.

The previous code was there because QuicSpdyStream uses spdy_session_ in its destructor. Since that is no longer true, QuicSpdySession destructor can be cleaned up too.

Protected by quic_reloadable_flag_quic_clean_up_spdy_session_destructor.

PiperOrigin-RevId: 331184986
Change-Id: I399b1093963f4da48dd0df766ceeac5966996d87

quic/core/http/quic_spdy_session.cc

diff --git a/quic/core/http/quic_spdy_session.cc b/quic/core/http/quic_spdy_session.cc
index 77a5a00..03eb235 100644
--- a/quic/core/http/quic_spdy_session.cc
+++ b/quic/core/http/quic_spdy_session.cc
@@ -414,6 +414,12 @@
   QUIC_BUG_IF(destruction_indicator_ != 123456789)
       << "QuicSpdyStream use after free. " << destruction_indicator_
       << QuicStackTrace();
+  destruction_indicator_ = 987654321;
+
+  if (GetQuicReloadableFlag(quic_clean_up_spdy_session_destructor)) {
+    QUIC_RELOADABLE_FLAG_COUNT(quic_clean_up_spdy_session_destructor);
+    return;
+  }
   // Set the streams' session pointers in closed and dynamic stream lists
   // to null to avoid subsequent use of this session.
   for (auto& stream : *closed_streams()) {
@@ -428,7 +434,6 @@
       static_cast<QuicSpdyStream*>(kv.second.get())->ClearSession();
     }
   }
-  destruction_indicator_ = 987654321;
 }
 
 void QuicSpdySession::Initialize() {

quic/core/http/quic_spdy_stream.h

diff --git a/quic/core/http/quic_spdy_stream.h b/quic/core/http/quic_spdy_stream.h
index ee15732..5a58842 100644
--- a/quic/core/http/quic_spdy_stream.h
+++ b/quic/core/http/quic_spdy_stream.h
@@ -209,6 +209,8 @@
 
   // Called when owning session is getting deleted to avoid subsequent
   // use of the spdy_session_ member.
+  // TODO(b/136274541): Remove this method once
+  // flag_quic_clean_up_spdy_session_destructor is deprecated.
   void ClearSession();
 
   // Returns true if the sequencer has delivered the FIN, and no more body bytes