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

Source/platform/WebThreadSupportingGC.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "platform/WebThreadSupportingGC.h"
 
 namespace blink {
 
-PassOwnPtr<WebThreadSupportingGC> WebThreadSupportingGC::create(const char* name)
-{
-    return adoptPtr(new WebThreadSupportingGC(name));
-}
+namespace {
 
-WebThreadSupportingGC::WebThreadSupportingGC(const char* name)
+class OwnWebThreadSupportingGC final : public WebThreadSupportingGC {
+    WTF_MAKE_NONCOPYABLE(OwnWebThreadSupportingGC);
+public:
+    explicit OwnWebThreadSupportingGC(const char* name);
+    ~OwnWebThreadSupportingGC() override;
+
+private:
+    WebThread& platformThread() const override
+    {
+        ASSERT(m_thread);
+        return *m_thread;
+    }
+    // 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;
+};
+
+OwnWebThreadSupportingGC::OwnWebThreadSupportingGC(const char* name)
     : m_thread(adoptPtr(Platform::current()->createThread(name)))
 {
 }
 
-WebThreadSupportingGC::~WebThreadSupportingGC()
+OwnWebThreadSupportingGC::~OwnWebThreadSupportingGC()
 {
     if (ThreadState::current()) {
         // WebThread's destructor blocks until all the tasks are processed.
         ThreadState::SafePointScope scope(ThreadState::HeapPointersOnStack);
         m_thread.clear();
     }
 }
 
+} // namespace
+
+PassOwnPtr<WebThreadSupportingGC> WebThreadSupportingGC::create(const char* name)
+{
+    return adoptPtr(new OwnWebThreadSupportingGC(name));
+}
+
+WebThreadSupportingGC::~WebThreadSupportingGC()
+{
+}
+
 void WebThreadSupportingGC::attachGC()
 {
+    ASSERT(platformThread().isCurrentThread());
     m_pendingGCRunner = adoptPtr(new PendingGCRunner);
     m_messageLoopInterruptor = adoptPtr(new MessageLoopInterruptor(&platformThread()));
     platformThread().addTaskObserver(m_pendingGCRunner.get());
     ThreadState::attach();
     ThreadState::current()->addInterruptor(m_messageLoopInterruptor.get());
 }
 
 void WebThreadSupportingGC::detachGC()
 {
+    ASSERT(platformThread().isCurrentThread());
     ThreadState::current()->removeInterruptor(m_messageLoopInterruptor.get());
     ThreadState::detach();
     platformThread().removeTaskObserver(m_pendingGCRunner.get());
     m_pendingGCRunner = nullptr;
     m_messageLoopInterruptor = nullptr;
 }
 
 } // namespace blink