bindings: Add C++ versions of WebIDL types and generalize NativeValueTraits.

third_party/WebKit/Source/bindings/core/v8/IDLTypesBase.h

Index: third_party/WebKit/Source/bindings/core/v8/IDLTypesBase.h
diff --git a/third_party/WebKit/Source/bindings/core/v8/IDLTypesBase.h b/third_party/WebKit/Source/bindings/core/v8/IDLTypesBase.h
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index 0000000000000000000000000000000000000000..42819078d81efd14c5a8f2978b7a25d11a32f810
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+++ b/third_party/WebKit/Source/bindings/core/v8/IDLTypesBase.h
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+// Copyright (c) 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 IDLTypesBase_h
+#define IDLTypesBase_h
+
+namespace blink {
+
+// This is the base type for all WebIDL types, such as the ones defined in
+// IDLTypes.h. It is defined in a separate location to avoid circular header
+// inclusions when one only needs to check if a type inherits from IDLBase.
+struct IDLBase {
+  using ImplType = void;
+};
+
+// If a child class returns a simple type known at the time it is declared, it
+// can inherit from IDLBaseHelper to avoid having to set ImplType on its own.
+//
+// Example:
+// struct MyType<double> final : public IDLBaseHelper<double> {};
+template <typename T>
+struct IDLBaseHelper : public IDLBase {
+  using ImplType = T;
+};
+
+}  // namespace blink
+
+#endif  // IDLTypesBase_h