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diff --git a/deps/v8/include/cppgc/custom-space.h b/deps/v8/include/cppgc/custom-space.h
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+++ b/deps/v8/include/cppgc/custom-space.h
@@ -0,0 +1,62 @@
+// Copyright 2020 the V8 project 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 INCLUDE_CPPGC_CUSTOM_SPACE_H_
+#define INCLUDE_CPPGC_CUSTOM_SPACE_H_
+
+#include <stddef.h>
+
+namespace cppgc {
+
+struct CustomSpaceIndex {
+  CustomSpaceIndex(size_t value) : value(value) {}  // NOLINT
+  size_t value;
+};
+
+/**
+ * Top-level base class for custom spaces. Users must inherit from CustomSpace
+ * below.
+ */
+class CustomSpaceBase {
+ public:
+  virtual ~CustomSpaceBase() = default;
+  virtual CustomSpaceIndex GetCustomSpaceIndex() const = 0;
+};
+
+/**
+ * Base class custom spaces should directly inherit from. The class inheriting
+ * from CustomSpace must define kSpaceIndex as unique space index. These
+ * indices need for form a sequence starting at 0.
+ *
+ * Example:
+ * \code
+ * class CustomSpace1 : public CustomSpace<CustomSpace1> {
+ *  public:
+ *   static constexpr CustomSpaceIndex kSpaceIndex = 0;
+ * };
+ * class CustomSpace2 : public CustomSpace<CustomSpace2> {
+ *  public:
+ *   static constexpr CustomSpaceIndex kSpaceIndex = 1;
+ * };
+ * \endcode
+ */
+template <typename ConcreteCustomSpace>
+class CustomSpace : public CustomSpaceBase {
+ public:
+  CustomSpaceIndex GetCustomSpaceIndex() const final {
+    return ConcreteCustomSpace::kSpaceIndex;
+  }
+};
+
+/**
+ * User-overridable trait that allows pinning types to custom spaces.
+ */
+template <typename T, typename = void>
+struct SpaceTrait {
+  using Space = void;
+};
+
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_CUSTOM_SPACE_H_