[NOT READY FOR REVIEW YET]workers: Some refactoring to allow creating new kind of worker threads

Source/platform/WebThreadSupportingGC.h

Index: Source/platform/WebThreadSupportingGC.h
diff --git a/Source/platform/WebThreadSupportingGC.h b/Source/platform/WebThreadSupportingGC.h
index 3c58d6de9aaab31763879d2a9acf7aa7586c6f03..495c083631c5003b51affedf08ce0ee8f2ef8610 100644
--- a/Source/platform/WebThreadSupportingGC.h
+++ b/Source/platform/WebThreadSupportingGC.h
@@ -21,68 +21,45 @@ namespace blink {
 // thread allocates any objects managed by the Blink GC. The detach GC
 // method must be called on the WebThread during shutdown when the thread
 // no longer needs to access objects managed by the Blink GC.
-class PLATFORM_EXPORT WebThreadSupportingGC final {
-    WTF_MAKE_NONCOPYABLE(WebThreadSupportingGC);
+class PLATFORM_EXPORT WebThreadSupportingGC {
 public:
     static PassOwnPtr<WebThreadSupportingGC> create(const char*);
-    ~WebThreadSupportingGC();
+
+    virtual ~WebThreadSupportingGC();
 
     void postTask(WebThread::Task* task)
     {
-        m_thread->postTask(task);
+        platformThread().postTask(task);
     }
 
     void postDelayedTask(WebThread::Task* task, long long delayMs)
     {
-        m_thread->postDelayedTask(task, delayMs);
+        platformThread().postDelayedTask(task, delayMs);
     }
 
     bool isCurrentThread() const
     {
-        return m_thread->isCurrentThread();
+        return platformThread().isCurrentThread();
     }
 
     void addTaskObserver(WebThread::TaskObserver* observer)
     {
-        m_thread->addTaskObserver(observer);
+        platformThread().addTaskObserver(observer);
     }
 
     void removeTaskObserver(WebThread::TaskObserver* observer)
     {
-        m_thread->removeTaskObserver(observer);
-    }
-
-    void enterRunLoop()
-    {
-        m_thread->enterRunLoop();
-    }
-
-    void exitRunLoop()
-    {
-        m_thread->exitRunLoop();
+        platformThread().removeTaskObserver(observer);
     }
 
     void attachGC();
     void detachGC();
 
-    WebThread& platformThread() const
-    {
-        ASSERT(m_thread);
-        return *m_thread;
-    }
+    virtual WebThread& platformThread() const = 0;
 
 private:
-    explicit WebThreadSupportingGC(const char*);
-
     OwnPtr<PendingGCRunner> m_pendingGCRunner;
     OwnPtr<MessageLoopInterruptor> m_messageLoopInterruptor;
-
-    // FIXME: This has to be last because of crbug.com/401397.
-    // A WorkerThread might get deleted before it had a chance to properly
-    // shut down. By deleting the WebThread first, we can guarantee that
-    // no pending tasks on the thread might want to access any of the other
-    // members during the WorkerThread's destruction.
-    OwnPtr<WebThread> m_thread;
 };
 
 }