Implement WebThreadSupportingGC, which wraps a WebThread attached to Oilpan's GC

Source/platform/WebThreadSupportingGC.h

Index: Source/platform/WebThreadSupportingGC.h
diff --git a/Source/platform/WebThreadSupportingGC.h b/Source/platform/WebThreadSupportingGC.h
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+++ b/Source/platform/WebThreadSupportingGC.h
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+// 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.
+
+#ifndef WebThreadSupportingGC_h
+#define WebThreadSupportingGC_h
+
+#include "platform/heap/glue/MessageLoopInterruptor.h"
+#include "platform/heap/glue/PendingGCRunner.h"
+#include "public/platform/Platform.h"
+#include "public/platform/WebThread.h"
+#include "wtf/Noncopyable.h"
+#include "wtf/OwnPtr.h"
+#include "wtf/PassOwnPtr.h"
+
+namespace blink {
+
+// WebThreadSupportingGC wraps a WebThread and adds support for attaching
+// to and detaching from the Blink GC infrastructure. The attachGC method
+// must be called during initialization on the WebThread and before the
+// 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 WebThreadSupportingGC {
+    WTF_MAKE_NONCOPYABLE(WebThreadSupportingGC);
+public:
+    static PassOwnPtr<WebThreadSupportingGC> create(const char*);
+
+    void postTask(WebThread::Task* task)
+    {
+        m_thread->postTask(task);

[jochen (gone - plz use gerrit), 2014/08/13 12:35:42]

this is not safe. on a worker thread, all posted tasks must be wrapped in some
wrapper class that checks the worker scope's state before execution. there's
another interface we use that has a postTask method that does the right
wrapping, something like WebWorkerRunLoop. can you piggyback on that?

[Mads Ager (chromium), 2014/08/13 12:40:37]

I'm not sure I understand. We are only replacing blink:WebThread in the code
base with WebThreadSupportingGC. So, where we call this postTask method we would
directly call blink::WebThread::postTask before. So, we will end up calling
exactly the same as we did before. Where does this become unsafe? I very well
might be missing something, but I don't see it.

+    }
+
+    void postDelayedTask(WebThread::Task* task, long long delayMs)
+    {
+        m_thread->postDelayedTask(task, delayMs);
+    }
+
+    bool isCurrentThread() const
+    {
+        return m_thread->isCurrentThread();
+    }
+
+    void addTaskObserver(WebThread::TaskObserver* observer)
+    {
+        m_thread->addTaskObserver(observer);
+    }
+
+    void removeTaskObserver(WebThread::TaskObserver* observer)
+    {
+        m_thread->removeTaskObserver(observer);
+    }
+
+    void enterRunLoop()
+    {
+        m_thread->enterRunLoop();
+    }
+
+    void exitRunLoop()
+    {
+        m_thread->exitRunLoop();
+    }
+
+    void attachGC();
+    void detachGC();
+
+    WebThread& platformThread() const
+    {
+        ASSERT(m_thread);
+        return *m_thread;
+    }
+
+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;
+};
+
+}
+
+#endif