Fix flaky test caused by the dependency of arena_ref.cc been destroyed before the destructor of ArenaRef was called

Author: cherylEnkidu

firestore/src/jni/arena_ref.cc

@@ -17,6 +17,7 @@
 #include "firestore/src/jni/arena_ref.h"
 
 #include <atomic>
+#include <utility>
 
 #include "firestore/src/android/firestore_android.h"
 #include "firestore/src/jni/env.h"
@@ -31,6 +32,9 @@ namespace jni {
 namespace {
 
 HashMap* gArenaRefHashMap = nullptr;
+jclass gHashMapClass = nullptr;
+jclass gLongClass = nullptr;
+jmethodID gLongConstructor = nullptr;
 std::mutex mutex_;
 
 int64_t GetNextArenaRefKey() {
@@ -115,7 +119,8 @@ ArenaRef::~ArenaRef() {
 }
 
 Local<Long> ArenaRef::key_object(Env& env) const {
-  return Long::Create(env, key_);
+  jobject key = env.get()->NewObject(gLongClass, gLongConstructor, key_);
+  return {env.get(), key};
 }
 
 void ArenaRef::Initialize(Env& env) {
@@ -124,6 +129,13 @@ void ArenaRef::Initialize(Env& env) {
   }
   Global<HashMap> hash_map(HashMap::Create(env));
   gArenaRefHashMap = new HashMap(hash_map.release());
+
+  gHashMapClass = env.get()->FindClass("java/util/HashMap");
+  gHashMapClass = static_cast<jclass>(env.get()->NewGlobalRef(gHashMapClass));
+
+  gLongClass = env.get()->FindClass("java/lang/Long");
+  gLongClass = static_cast<jclass>(env.get()->NewGlobalRef(gLongClass));
+  gLongConstructor = env.get()->GetMethodID(gLongClass, "<init>", "(J)V");
 }
 
 Local<Object> ArenaRef::get(Env& env) const {