Fix test failures of IDBTransactionTest.EnsureLifetime with ENABLE(OILPAN)

Source/modules/indexeddb/IDBRequestTest.cpp

Index: Source/modules/indexeddb/IDBRequestTest.cpp
diff --git a/Source/modules/indexeddb/IDBRequestTest.cpp b/Source/modules/indexeddb/IDBRequestTest.cpp
index 2ddbf31440b5f2e9018c144942a76a75ce6eaed6..de4c20cb89a7909225a92052fbe5f7f27fbbd8de 100644
--- a/Source/modules/indexeddb/IDBRequestTest.cpp
+++ b/Source/modules/indexeddb/IDBRequestTest.cpp
@@ -75,8 +75,14 @@ class IDBRequestTest : public testing::Test {
 public:
     IDBRequestTest()
         : m_scope(v8::Isolate::GetCurrent())
+        , m_executionContext(adoptRef(new NullExecutionContext()))
     {
-        m_scope.scriptState()->setExecutionContext(adoptRef(new NullExecutionContext()));
+        m_scope.scriptState()->setExecutionContext(m_executionContext.get());
+    }
+
+    ~IDBRequestTest()
+    {
+        m_scope.scriptState()->setExecutionContext(0);
     }
 
     v8::Isolate* isolate() const { return m_scope.isolate(); }
@@ -85,6 +91,7 @@ public:
 
 private:
     V8TestingScope m_scope;
+    RefPtr<ExecutionContext> m_executionContext;
 };
 
 TEST_F(IDBRequestTest, EventsAfterStopping)