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 "public/platform/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.
+// WebPassOwnPtr<T> is destructible on chromium side only when it contains
+// nullptr.
+// TODO(yhirano): Migrate to scoped_ptr or std::unique_ptr once the repository
+// merge is done or C++11 std library is allowed.
+template <typename T>
+class WebPassOwnPtr final {
+public:
+    WebPassOwnPtr() : m_ptr(nullptr) {}
+    WebPassOwnPtr(decltype(nullptr)) : m_ptr(nullptr) {}
+    // We need |const| to bind an rvalue. As a result, |m_ptr| needs to be
+    // mutable because we manipulate it.
+    template <typename U>
+    WebPassOwnPtr(const WebPassOwnPtr<U>& o)
+    {
+        m_ptr = o.m_ptr;
+        o.m_ptr = nullptr;
+    }
+    ~WebPassOwnPtr()
+    {
+#if INSIDE_BLINK
+        release();
+#endif
+        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) {}
+
+    // See the constructor comment to see why |mutable| is needed.
+    mutable T* m_ptr;
+};
+
+template <typename T>
+WebPassOwnPtr<T> adoptWebPtr(T* p) { return WebPassOwnPtr<T>(p); }
+
+} // namespace blink
+
+#endif