低版本v8，ScriptObject或者Delegate引用的js对象不释放的问题，原因是v8::Persistent析构不会自动Reset，改为v8::Global可以解决问题

Author: chexiongsheng

unity/native/papi-v8/source/PesapiV8Impl.cpp

@@ -30,7 +30,7 @@ struct pesapi_env_ref__
     {
     }
 
-    v8::Persistent<v8::Context> context_persistent;
+    v8::Global<v8::Context> context_persistent;
     v8::Isolate* const isolate;
     int ref_count;
     std::weak_ptr<int> env_life_cycle_tracker;
@@ -43,7 +43,7 @@ struct pesapi_value_ref__ : pesapi_env_ref__
     {
     }
 
-    v8::Persistent<v8::Value> value_persistent;
+    v8::Global<v8::Value> value_persistent;
     uint32_t internal_field_count;
     void* internal_fields[0];
 };

unity/test/Src/Cases/Javascript/CrossLang/CrossLangTest.cs

@@ -3114,5 +3114,64 @@ public void TestInOutStringRefParam()
             ");
         }
 
+
+        public void CreateJsObjects()
+        {
+            var jsEnv = UnitTestEnv.GetEnv();
+            jsEnv.Eval("global.__weak_ref_arr = []");
+
+            for (int i = 0; i < 10; i++)
+            {
+                jsEnv.Eval<ScriptObject>(@"
+                var test_val_weak = new WeakRef({a:1});
+                global.__weak_ref_arr.push(test_val_weak)
+                test_val_weak.deref();");
+            }
+        }
+
+        [Test]
+        public void JsObjectCollectTest()
+        {
+            CreateJsObjects();
+
+            GC.Collect();
+            GC.WaitForPendingFinalizers();
+
+            var jsEnv = UnitTestEnv.GetEnv();
+            jsEnv.Tick();
+            jsEnv.Backend.LowMemoryNotification();
+
+            Assert.AreNotEqual(0, jsEnv.Eval<int>("global.__weak_ref_arr.filter(e => e.deref() === undefined).length"));
+        }
+
+        public void CreateDelegate()
+        {
+            var jsEnv = UnitTestEnv.GetEnv();
+            jsEnv.Eval("global.__weak_ref_arr = []");
+
+            for (int i = 0; i < 10; i++)
+            {
+                jsEnv.Eval<Action>(@"
+                var test_val_weak = new WeakRef(() => {});
+                global.__weak_ref_arr.push(test_val_weak)
+                test_val_weak.deref();");
+            }
+        }
+
+        [Test]
+        public void DelegateCollectTest()
+        {
+            CreateDelegate();
+
+            GC.Collect();
+            GC.WaitForPendingFinalizers();
+
+            var jsEnv = UnitTestEnv.GetEnv();
+            jsEnv.Tick();
+            jsEnv.Backend.LowMemoryNotification();
+
+            Assert.AreNotEqual(0, jsEnv.Eval<int>("global.__weak_ref_arr.filter(e => e.deref() === undefined).length"));
+        }
+
     }
 }