Introduce WebPassOwnPtr.

public/platform/WebPassOwnPtr.h

+// Copyright 2015 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 WebPassOwnPtr_h
+#define WebPassOwnPtr_h
+
+#include "WebCommon.h"
+
+#if INSIDE_BLINK
+#include "wtf/PassOwnPtr.h"
+#endif
+
+namespace blink {
+
+// WebPassOwnPtr<T> is used to pass a T pointer with ownership from chromium
+// side to blink side.

[kinuko, 2015/07/16 06:49:35]

Add a comment to note that the ownership must be taken by calling release() in
the blink implementation before it gets destructed?

[yhirano, 2015/07/16 07:27:02]

I think implicit release is useful inside blink. What do you think?

+template <typename T>
+class WebPassOwnPtr {
+public:
+    WebPassOwnPtr() : m_ptr(nullptr) {}
+    WebPassOwnPtr(decltype(nullptr)) : m_ptr(nullptr) {}
+    template <typename U>
+    WebPassOwnPtr(const WebPassOwnPtr<U>& o)
+    {
+        m_ptr = o.m_ptr;
+        o.m_ptr = nullptr;
+    }
+    ~WebPassOwnPtr() { BLINK_ASSERT(!m_ptr); }
+    WebPassOwnPtr& operator =(const WebPassOwnPtr&) = delete;
+
+#if INSIDE_BLINK
+    PassOwnPtr<T> release()
+    {
+        T* ptr = m_ptr;
+        m_ptr = nullptr;
+        return adoptPtr(ptr);
+    }
+#endif // INSIDE_BLINK
+
+    template <typename U> friend class WebPassOwnPtr;
+    template <typename U> friend WebPassOwnPtr<U> adoptWebPtr(U*);
+
+private:
+    explicit WebPassOwnPtr(T* ptr) : m_ptr(ptr) {}
+
+    mutable T* m_ptr;
+};
+
+template <typename T>
+WebPassOwnPtr<T> adoptWebPtr(T* p) { return WebPassOwnPtr<T>(p); }
+
+} // namespace blink
+
+#endif