Oilpan: provide a weak 'this' pointer abstraction for cancellable closures.

third_party/WebKit/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 1281 matching lines @@
     void assign(Self* self)
     {
         ASSERT(!m_keepAlive || m_keepAlive.get() == self);
         m_keepAlive = self;
     }
 
     GC_PLUGIN_IGNORE("420515")
     Persistent<Self> m_keepAlive;
 };
 
+// Only a very reduced form of weak heap object references can currently be held
+// by WTF::Closure<>s. i.e., bound as a 'this' pointer only.
+//
+// TODO(sof): once wtf/Functional.h is able to work over platform/heap/ types
+// (like CrossThreadWeakPersistent<>), drop the restriction on weak persistent
+// use by function closures (and rename this ad-hoc type.)
 template<typename T>
-class AllowCrossThreadWeakPersistent {
+class CrossThreadWeakPersistentThisPointer {
     STACK_ALLOCATED();
 public:
-    explicit AllowCrossThreadWeakPersistent(T* value) : m_value(value) { }
+    explicit CrossThreadWeakPersistentThisPointer(T* value) : m_value(value) { }
     CrossThreadWeakPersistent<T> value() const { return m_value; }
 private:
     CrossThreadWeakPersistent<T> m_value;
 };
 
 // LEAK_SANITIZER_DISABLED_SCOPE: all allocations made in the current scope
 // will be exempted from LSan consideration.
 //
 // TODO(sof): move this to wtf/LeakAnnotations.h (LeakSanitizer.h?) once
 // wtf/ can freely call upon Oilpan functionality.
@@ skipping 245 matching lines @@
 struct ParamStorageTraits<T*> : public PointerParamStorageTraits<T*, blink::IsGarbageCollectedType<T>::value> {
     static_assert(sizeof(T), "T must be fully defined");
 };
 
 template<typename T>
 struct ParamStorageTraits<RawPtr<T>> : public PointerParamStorageTraits<T*, blink::IsGarbageCollectedType<T>::value> {
     static_assert(sizeof(T), "T must be fully defined");
 };
 
 template<typename T>
-struct ParamStorageTraits<blink::AllowCrossThreadWeakPersistent<T>> {
+struct ParamStorageTraits<blink::CrossThreadWeakPersistentThisPointer<T>> {
     static_assert(sizeof(T), "T must be fully defined");
     using StorageType = blink::CrossThreadWeakPersistent<T>;
 
-    static StorageType wrap(const blink::AllowCrossThreadWeakPersistent<T>& value) { return value.value(); }
+    static StorageType wrap(const blink::CrossThreadWeakPersistentThisPointer<T>& value) { return value.value(); }
 
-    // Currently assume that the call sites of this unwrap() account for cleared weak references also.
-    // TODO(sof): extend WTF::FunctionWrapper call overloading to also handle (CrossThread)WeakPersistent.
-    static T* unwrap(const StorageType& value) { return value.get(); }
+    // WTF::FunctionWrapper<> handles WeakPtr<>, so recast this weak persistent
+    // into it.
+    //
+    // TODO(sof): remove this hack once wtf/Functional.h can also work with a type like
+    // CrossThreadWeakPersistent<>.
+    static WeakPtr<T> unwrap(const StorageType& value) { return WeakPtr<T>(WeakReference<T>::create(value.get())); }
 };
 
 template<typename T>
 PassRefPtr<T> adoptRef(blink::RefCountedGarbageCollected<T>*) = delete;
 
 } // namespace WTF
 
 #endif