Introduce WorkerThread::willShutdown()

Source/core/workers/WorkerThreadTest.cpp

Index: Source/core/workers/WorkerThreadTest.cpp
diff --git a/Source/core/workers/WorkerThreadTest.cpp b/Source/core/workers/WorkerThreadTest.cpp
index 9a88e0188365934c96c042624e118e821befa4de..dfed5670dc2b676c174c5d61dd63bcbef2ca605d 100644
--- a/Source/core/workers/WorkerThreadTest.cpp
+++ b/Source/core/workers/WorkerThreadTest.cpp
@@ -111,11 +111,11 @@ public:
     {
         return *m_thread;
     }
-    void willDestroyIsolate() override
+    void willShutdown() override
     {
         v8::Isolate::GetCurrent()->RequestGarbageCollectionForTesting(v8::Isolate::kFullGarbageCollection);
         Heap::collectAllGarbage();
-        WorkerThread::willDestroyIsolate();
+        WorkerThread::willShutdown();
     }
 
     MOCK_METHOD1(doIdleGc, bool(double deadlineSeconds));