Oilpan: lazily create SelfKeepAlive<>'s persistent reference.

Source/platform/heap/Handle.h

 /*
  * Copyright (C) 2014 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 913 matching lines @@
 //     SelfKeepAlive m_keepAlive;
 //  };
 //
 // The responsibility to call clear() in a timely fashion resides with the implementation
 // of the object.
 //
 //
 template<typename Self>
 class SelfKeepAlive {
 public:
+    SelfKeepAlive()
+    {
+    }
+
+    explicit SelfKeepAlive(Self* self)
+    {
+        assign(self);
+    }
+
     SelfKeepAlive& operator=(Self* self)
     {
-        ASSERT(!m_keepAlive || m_keepAlive.get() == self);
-        m_keepAlive = self;
+        assign(self);
         return *this;
     }
 
     void clear()
     {
-        m_keepAlive = nullptr;
+        m_keepAlive.clear();
     }
 
-    typedef Persistent<Self> (SelfKeepAlive::*UnspecifiedBoolType);
+    typedef OwnPtr<Persistent<Self>> (SelfKeepAlive::*UnspecifiedBoolType);
     operator UnspecifiedBoolType() const { return m_keepAlive ? &SelfKeepAlive::m_keepAlive : 0; }
 
 private:
+    void assign(Self* self)
+    {
+        ASSERT(!m_keepAlive || m_keepAlive->get() == self);
+        if (!m_keepAlive)
+            m_keepAlive = adoptPtr(new Persistent<Self>);
+        *m_keepAlive = self;
+    }
+
     GC_PLUGIN_IGNORE("420515")
-    Persistent<Self> m_keepAlive;
+    OwnPtr<Persistent<Self>> m_keepAlive;
 };
 
 } // namespace blink
 
 namespace WTF {
 
 template <typename T> struct VectorTraits<blink::Member<T>> : VectorTraitsBase<blink::Member<T>> {
     static const bool needsDestruction = false;
     static const bool canInitializeWithMemset = true;
     static const bool canClearUnusedSlotsWithMemset = true;
@@ skipping 178 matching lines @@
 struct ParamStorageTraits<RawPtr<T>> : public PointerParamStorageTraits<T*, blink::IsGarbageCollectedType<T>::value> {
     static_assert(sizeof(T), "T must be fully defined");
 };
 
 template<typename T>
 PassRefPtr<T> adoptRef(blink::RefCountedGarbageCollected<T>*) = delete;
 
 } // namespace WTF
 
 #endif