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

third_party/WebKit/Source/platform/heap/Handle.h

Index: third_party/WebKit/Source/platform/heap/Handle.h
diff --git a/third_party/WebKit/Source/platform/heap/Handle.h b/third_party/WebKit/Source/platform/heap/Handle.h
index 49d3f33e2e717c08c92c3d0f119052c99b777240..d0238d094600b4e0a118c79318f7065dd1d8a1af 100644
--- a/third_party/WebKit/Source/platform/heap/Handle.h
+++ b/third_party/WebKit/Source/platform/heap/Handle.h
@@ -1300,10 +1300,10 @@ private:
 };
 
 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;
@@ -1569,15 +1569,15 @@ struct ParamStorageTraits<RawPtr<T>> : public PointerParamStorageTraits<T*, blin
 };
 
 template<typename T>
-struct ParamStorageTraits<blink::AllowCrossThreadWeakPersistent<T>> {
+struct ParamStorageTraits<blink::CrossThreadWeakPersistentThisPointer<T>> {

[haraken, 2016/01/12 00:04:57]

CrossThreadWeakPersistentThisPointer => WeakPersistentForFunctionBind ?

[sof, 2016/01/12 07:23:40]

That name promises a little bit more than I want it to,
WeakPersistentThisPointerForFunctionBind ?

(i.e., we shouldn't support weak persistents elsewhere in closures until
wtf/Functional.h can work with (CrossThread)(Weak)Persistents properly.)

     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.
+    static WeakPtr<T> unwrap(const StorageType& value) { return WeakPtr<T>(WeakReference<T>::create(value.get())); }
 };
 
 template<typename T>