[end2end] Fix fuzzer found memory leak (#33264)

(this is a bug in the core e2e fuzzer infrastructure)

test/core/end2end/end2end_test_corpus/clusterfuzz-testcase-minimized-core_end2end_test_fuzzer-4592933739233280

@@ -0,0 +1,7 @@
+test_id: 3405774848
+event_engine_actions {
+  run_delay: 0
+  run_delay: 6399
+  run_delay: 4294967296
+  run_delay: 4294967296
+}

test/core/end2end/end2end_tests.cc

@@ -84,6 +84,13 @@ void CoreEnd2endTest::SetUp() {
 
 void CoreEnd2endTest::TearDown() {
   const bool do_shutdown = fixture_ != nullptr;
+  std::shared_ptr<grpc_event_engine::experimental::EventEngine> ee;
+// TODO(hork): locate the windows leak so we can enable end2end experiments.
+#ifndef GPR_WINDOWS
+  if (grpc_is_initialized()) {
+    ee = grpc_event_engine::experimental::GetDefaultEventEngine();
+  }
+#endif
   ShutdownAndDestroyClient();
   ShutdownAndDestroyServer();
   cq_verifier_.reset();
@@ -98,15 +105,11 @@ void CoreEnd2endTest::TearDown() {
     cq_ = nullptr;
   }
   fixture_.reset();
-// TODO(hork): locate the windows leak so we can enable end2end experiments.
-#ifndef GPR_WINDOWS
   // Creating an EventEngine requires gRPC initialization, which the NoOp test
   // does not do. Skip the EventEngine check if unnecessary.
-  if (grpc_is_initialized()) {
-    quiesce_event_engine_(
-        grpc_event_engine::experimental::GetDefaultEventEngine());
+  if (ee != nullptr) {
+    quiesce_event_engine_(std::move(ee));
   }
-#endif
   if (do_shutdown) {
     grpc_shutdown_blocking();
     // This will wait until gRPC shutdown has actually happened to make sure

test/core/event_engine/event_engine_test_utils.cc

@@ -75,7 +75,7 @@ std::string GetNextSendMessage() {
   return tmp_s;
 }
 
-void WaitForSingleOwner(std::shared_ptr<EventEngine>&& engine) {
+void WaitForSingleOwner(std::shared_ptr<EventEngine> engine) {
   while (engine.use_count() > 1) {
     GRPC_LOG_EVERY_N_SEC(2, GPR_INFO, "engine.use_count() = %ld",
                          engine.use_count());

test/core/event_engine/event_engine_test_utils.h

@@ -47,7 +47,9 @@ std::string GetNextSendMessage();
 
 // Waits until the use_count of the EventEngine shared_ptr has reached 1
 // and returns.
-void WaitForSingleOwner(std::shared_ptr<EventEngine>&& engine);
+// Callers must give up their ref, or this method will block forever.
+// Usage: WaitForSingleOwner(std::move(engine))
+void WaitForSingleOwner(std::shared_ptr<EventEngine> engine);
 
 // A helper method to exchange data between two endpoints. It is assumed
 // that both endpoints are connected. The data (specified as a string) is