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

Source/platform/WebThreadSupportingGC.cpp

Index: Source/platform/WebThreadSupportingGC.cpp
diff --git a/Source/platform/WebThreadSupportingGC.cpp b/Source/platform/WebThreadSupportingGC.cpp
index df76335a69473b83aed6c4e6dd002bd3b9652250..e2ea27ddf183add2a2821e4e72841d6c3de1f5b3 100644
--- a/Source/platform/WebThreadSupportingGC.cpp
+++ b/Source/platform/WebThreadSupportingGC.cpp
@@ -7,17 +7,34 @@
 
 namespace blink {
 
-PassOwnPtr<WebThreadSupportingGC> WebThreadSupportingGC::create(const char* name)
-{
-    return adoptPtr(new WebThreadSupportingGC(name));
-}
+namespace {
+
+class OwnWebThreadSupportingGC final : public WebThreadSupportingGC {
+    WTF_MAKE_NONCOPYABLE(OwnWebThreadSupportingGC);
+public:
+    explicit OwnWebThreadSupportingGC(const char* name);
+    ~OwnWebThreadSupportingGC() override;
 
-WebThreadSupportingGC::WebThreadSupportingGC(const char* name)
+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.
@@ -26,8 +43,20 @@ WebThreadSupportingGC::~WebThreadSupportingGC()
     }
 }
 
+} // 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());
@@ -37,6 +66,7 @@ void WebThreadSupportingGC::attachGC()
 
 void WebThreadSupportingGC::detachGC()
 {
+    ASSERT(platformThread().isCurrentThread());
     ThreadState::current()->removeInterruptor(m_messageLoopInterruptor.get());
     ThreadState::detach();
     platformThread().removeTaskObserver(m_pendingGCRunner.get());