refactor: EventEmitters without gin_helper (#22726)

shell/browser/event_emitter_mixin.h

@@ -0,0 +1,78 @@
+// Copyright (c) 2019 Slack Technologies, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef SHELL_BROWSER_EVENT_EMITTER_MIXIN_H_
+#define SHELL_BROWSER_EVENT_EMITTER_MIXIN_H_
+
+#include <utility>
+
+#include "gin/object_template_builder.h"
+#include "shell/common/gin_helper/event_emitter.h"
+
+namespace gin_helper {
+
+namespace internal {
+v8::Local<v8::FunctionTemplate> GetEventEmitterTemplate(v8::Isolate* isolate);
+}  // namespace internal
+
+template <typename T>
+class EventEmitterMixin {
+ public:
+  // this.emit(name, new Event(), args...);
+  template <typename... Args>
+  bool Emit(base::StringPiece name, Args&&... args) {
+    v8::Isolate* isolate = v8::Isolate::GetCurrent();
+    v8::Locker locker(isolate);
+    v8::HandleScope handle_scope(isolate);
+    v8::Local<v8::Object> wrapper;
+    if (!static_cast<T*>(this)->GetWrapper(isolate).ToLocal(&wrapper))
+      return false;
+    v8::Local<v8::Object> event = internal::CreateEvent(isolate, wrapper);
+    return EmitWithEvent(isolate, wrapper, name, event,
+                         std::forward<Args>(args)...);
+  }
+
+ protected:
+  EventEmitterMixin() = default;
+
+  gin::ObjectTemplateBuilder GetObjectTemplateBuilder(v8::Isolate* isolate) {
+    gin::PerIsolateData* data = gin::PerIsolateData::From(isolate);
+    auto* wrapper_info = &(static_cast<T*>(this)->kWrapperInfo);
+    v8::Local<v8::FunctionTemplate> constructor =
+        data->GetFunctionTemplate(wrapper_info);
+    if (constructor.IsEmpty()) {
+      constructor = v8::FunctionTemplate::New(isolate);
+      constructor->Inherit(internal::GetEventEmitterTemplate(isolate));
+      data->SetFunctionTemplate(wrapper_info, constructor);
+    }
+    return gin::ObjectTemplateBuilder(isolate,
+                                      static_cast<T*>(this)->GetTypeName(),
+                                      constructor->InstanceTemplate());
+  }
+
+ private:
+  // this.emit(name, event, args...);
+  template <typename... Args>
+  static bool EmitWithEvent(v8::Isolate* isolate,
+                            v8::Local<v8::Object> wrapper,
+                            base::StringPiece name,
+                            v8::Local<v8::Object> event,
+                            Args&&... args) {
+    auto context = isolate->GetCurrentContext();
+    gin_helper::EmitEvent(isolate, wrapper, name, event,
+                          std::forward<Args>(args)...);
+    v8::Local<v8::Value> defaultPrevented;
+    if (event->Get(context, gin::StringToV8(isolate, "defaultPrevented"))
+            .ToLocal(&defaultPrevented)) {
+      return defaultPrevented->BooleanValue(isolate);
+    }
+    return false;
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(EventEmitterMixin);
+};
+
+}  // namespace gin_helper
+
+#endif  // SHELL_BROWSER_EVENT_EMITTER_MIXIN_H_