Revert r189385 "Remove LifecycleContext" and r189391, r189530, r189456 that block it

Source/platform/LifecycleContext.h

Index: Source/platform/LifecycleContext.h
diff --git a/Source/platform/LifecycleContext.h b/Source/platform/LifecycleContext.h
new file mode 100644
index 0000000000000000000000000000000000000000..c48423a3b57f015e4fc22aecaa64a4600e230b71
--- /dev/null
+++ b/Source/platform/LifecycleContext.h
@@ -0,0 +1,104 @@
+
+/*
+ * Copyright (C) 2013 Google Inc. All Rights Reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef LifecycleContext_h
+#define LifecycleContext_h
+
+#include "platform/LifecycleNotifier.h"
+#include "platform/LifecycleObserver.h"
+#include "wtf/HashSet.h"
+#include "wtf/OwnPtr.h"
+#include "wtf/PassOwnPtr.h"
+
+namespace blink {
+
+class Visitor;
+
+template <typename T>
+class LifecycleContext {
+public:
+    typedef LifecycleNotifier<T> Notifier;
+    typedef LifecycleObserver<T> Observer;
+
+    LifecycleContext() { }
+    virtual ~LifecycleContext() { }
+
+    virtual bool isContextThread() const { return true; }
+
+    virtual void notifyContextDestroyed()
+    {
+        lifecycleNotifier().notifyContextDestroyed();
+    }
+
+    // Called from the constructor of observers.
+    void wasObservedBy(Observer*);
+
+    // Called from the destructor of observers.
+    void wasUnobservedBy(Observer*);
+
+    virtual void trace(Visitor*) { }
+
+protected:
+    Notifier& lifecycleNotifier();
+
+private:
+    PassOwnPtr<Notifier> createLifecycleNotifier();
+
+    OwnPtr<Notifier> m_lifecycleNotifier;
+};
+
+template<typename T>
+inline void LifecycleContext<T>::wasObservedBy(typename LifecycleContext<T>::Observer* observer)
+{
+    ASSERT(isContextThread());
+    lifecycleNotifier().addObserver(observer);
+}
+
+template<typename T>
+inline void LifecycleContext<T>::wasUnobservedBy(typename LifecycleContext<T>::Observer* observer)
+{
+    ASSERT(isContextThread());
+    lifecycleNotifier().removeObserver(observer);
+}
+
+template<typename T>
+inline typename LifecycleContext<T>::Notifier& LifecycleContext<T>::lifecycleNotifier()
+{
+    if (!m_lifecycleNotifier)
+        m_lifecycleNotifier = static_cast<T*>(this)->createLifecycleNotifier();
+    return *m_lifecycleNotifier;
+}
+
+template<typename T>
+inline PassOwnPtr<typename LifecycleContext<T>::Notifier> LifecycleContext<T>::createLifecycleNotifier()
+{
+    return LifecycleContext<T>::Notifier::create(static_cast<T*>(this));
+}
+
+} // namespace blink
+
+#endif // LifecycleContext_h