workers: Move ownership of WebThread from WorkerThread

Source/core/workers/WorkerThreadStartupData.h

Index: Source/core/workers/WorkerThreadStartupData.h
diff --git a/Source/core/workers/WorkerThreadStartupData.h b/Source/core/workers/WorkerThreadStartupData.h
index 36c5d22f7ee769559a4f1d730a32948d70dbaa37..fb7e48ac8f6eff4d3d9ddb6159691d71141fbe42 100644
--- a/Source/core/workers/WorkerThreadStartupData.h
+++ b/Source/core/workers/WorkerThreadStartupData.h
@@ -43,6 +43,7 @@
 
 namespace blink {
 
+class WebThreadSupportingGC;
 class WorkerClients;
 
 class CORE_EXPORT WorkerThreadStartupData final {
@@ -90,6 +91,8 @@ public:
 
     V8CacheOptions m_v8CacheOptions;
 
+    WebThreadSupportingGC* m_thread;
+
 private:
     WorkerThreadStartupData(const KURL& scriptURL, const String& userAgent, const String& sourceCode, PassOwnPtr<Vector<char>> cachedMetaData, WorkerThreadStartMode, const String& contentSecurityPolicy, ContentSecurityPolicyHeaderType contentSecurityPolicyType, const SecurityOrigin*, PassOwnPtrWillBeRawPtr<WorkerClients>, V8CacheOptions);
 };