[SharedArrayBuffer] Prevent SharedArrayBuffer being used in Web APIs

third_party/WebKit/Source/core/dom/MaybeShared.h

Index: third_party/WebKit/Source/core/dom/MaybeShared.h
diff --git a/third_party/WebKit/Source/core/dom/MaybeShared.h b/third_party/WebKit/Source/core/dom/MaybeShared.h
new file mode 100644
index 0000000000000000000000000000000000000000..5e376765ca5cb6b3ddc7e39a923e9ac012721a2b
--- /dev/null
+++ b/third_party/WebKit/Source/core/dom/MaybeShared.h
@@ -0,0 +1,54 @@
+// Copyright 2017 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 MaybeShared_h
+#define MaybeShared_h
+
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+template <typename T>
+class CORE_EXPORT MaybeShared {
+  STACK_ALLOCATED();
+
+ public:
+  MaybeShared() {}
+
+  MaybeShared(T* typedArray) : m_typedArray(typedArray) {}
+  MaybeShared(const MaybeShared& other) = default;
+  template <typename U>
+  MaybeShared(const MaybeShared<U>& other)
+      : m_typedArray(other.viewMaybeShared()) {}
+
+  MaybeShared& operator=(T* typedArray) {
+    m_typedArray = typedArray;
+    return *this;
+  }
+  MaybeShared& operator=(const MaybeShared& other) = default;
+  template <typename U>
+  MaybeShared& operator=(const MaybeShared<U>& other) {
+    m_typedArray = other.viewMaybeShared();
+    return *this;
+  }
+
+  bool isShared() const { return m_typedArray->view()->isShared(); }
+
+  T* viewNotShared() const {
+    DCHECK(!isShared());
+    return m_typedArray.get();
+  }
+  T* viewMaybeShared() const { return m_typedArray.get(); }
+
+  bool operator!() const { return !m_typedArray; }
+  explicit operator bool() const { return !!m_typedArray; }
+  operator ScriptWrappable*() const { return m_typedArray.get(); }
+
+ private:
+  Member<T> m_typedArray;
+};
+
+}  // namespace blink
+
+#endif  // MaybeShared_h