CodeGen: Define bindings::UnionBase for generated union type definitions

Bug: 839389
Change-Id: I916e7fa8ec6e39a3637090aaef3a24b4c45dcf57
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2012361Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Hitoshi Yoshida <peria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733947}

third_party/blink/renderer/bindings/core/v8/native_value_traits_impl.h

@@ -27,6 +27,7 @@ struct WrapperTypeInfo;
 namespace bindings {
 
 class DictionaryBase;
+class UnionBase;
 
 CORE_EXPORT ScriptWrappable* NativeValueTraitsInterfaceNativeValue(
     v8::Isolate* isolate,
@@ -789,6 +790,19 @@ struct NativeValueTraits<
   }
 };
 
+// Union type
+template <typename T>
+struct NativeValueTraits<
+    T,
+    typename std::enable_if_t<std::is_base_of<bindings::UnionBase, T>::value>>
+    : public NativeValueTraitsBase<T*> {
+  static T NativeValue(v8::Isolate* isolate,
+                       v8::Local<v8::Value> value,
+                       ExceptionState& exception_state) {
+    return T::Create(isolate, value, exception_state);
+  }
+};
+
 // Nullable
 template <typename InnerType>
 struct NativeValueTraits<

third_party/blink/renderer/platform/BUILD.gn

@@ -434,6 +434,7 @@ jumbo_component("platform") {
     "bindings/trace_wrapper_v8_reference.h",
     "bindings/trace_wrapper_v8_string.cc",
     "bindings/trace_wrapper_v8_string.h",
+    "bindings/union_base.h",
     "bindings/v0_custom_element_binding.cc",
     "bindings/v0_custom_element_binding.h",
     "bindings/v8_binding.cc",

third_party/blink/renderer/platform/bindings/to_v8.h

@@ -19,6 +19,7 @@
 #include "third_party/blink/renderer/platform/bindings/dom_data_store.h"
 #include "third_party/blink/renderer/platform/bindings/script_state.h"
 #include "third_party/blink/renderer/platform/bindings/script_wrappable.h"
+#include "third_party/blink/renderer/platform/bindings/union_base.h"
 #include "third_party/blink/renderer/platform/bindings/v8_binding.h"
 #include "third_party/blink/renderer/platform/wtf/forward.h"
 #include "third_party/blink/renderer/platform/wtf/std_lib_extras.h"
@@ -85,6 +86,17 @@ inline v8::Local<v8::Value> ToV8(CallbackInterfaceBase* callback,
                   : v8::Null(isolate).As<v8::Value>();
 }
 
+// Union type
+
+inline v8::Local<v8::Value> ToV8(const bindings::UnionBase& value,
+                                 v8::Local<v8::Object> creation_context,
+                                 v8::Isolate* isolate) {
+  v8::Local<v8::Value> v8_value =
+      value.CreateV8Object(isolate, creation_context);
+  DCHECK(!v8_value.IsEmpty());
+  return v8_value;
+}
+
 // Primitives
 
 inline v8::Local<v8::Value> ToV8(const String& value,

third_party/blink/renderer/platform/bindings/union_base.h

+// Copyright 2020 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 THIRD_PARTY_BLINK_RENDERER_PLATFORM_BINDINGS_UNION_BASE_H_
+#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_BINDINGS_UNION_BASE_H_
+
+#include "third_party/blink/renderer/platform/heap/handle.h"
+#include "third_party/blink/renderer/platform/platform_export.h"
+#include "v8/include/v8.h"
+
+namespace blink {
+
+class Visitor;
+
+namespace bindings {
+
+// This class is the base class for all IDL dictionary implementations.  This
+// is designed to collaborate with NativeValueTraits and ToV8 with supporting
+// type dispatching (SFINAE, etc.).
+class PLATFORM_EXPORT UnionBase {
+  DISALLOW_NEW();
+
+ public:
+  virtual ~UnionBase() = default;
+
+  virtual v8::Local<v8::Value> CreateV8Object(
+      v8::Isolate* isolate,
+      v8::Local<v8::Object> creation_context) const = 0;
+
+  void Trace(Visitor*) {}
+
+ protected:
+  UnionBase() = default;
+  UnionBase(const UnionBase&) = default;
+  UnionBase(UnionBase&&) = default;
+  UnionBase& operator=(const UnionBase&) = default;
+  UnionBase& operator=(UnionBase&&) = default;
+};
+
+}  // namespace bindings
+
+}  // namespace blink
+
+#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_BINDINGS_UNION_BASE_H_