ui: Cleanup class/struct forward declarations

extensions/renderer/event_emitter.h

Index: extensions/renderer/event_emitter.h
diff --git a/extensions/renderer/event_emitter.h b/extensions/renderer/event_emitter.h
new file mode 100644
index 0000000000000000000000000000000000000000..ee59f6d4c0df7e814083ac3fd05a000f4bf910fe
--- /dev/null
+++ b/extensions/renderer/event_emitter.h
@@ -0,0 +1,51 @@
+// Copyright 2016 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 EXTENSIONS_RENDERER_EVENT_EMITTER_H_
+#define EXTENSIONS_RENDERER_EVENT_EMITTER_H_
+
+#include <vector>
+
+#include "gin/wrappable.h"
+#include "v8/include/v8.h"
+
+namespace gin {
+class Arguments;
+}
+
+namespace extensions {
+
+// A gin::Wrappable Event object. One is expected to be created per event, per
+// context. Note: this object *does not* clear any events, so it must be
+// destroyed with the context to avoid leaking.
+class EventEmitter final : public gin::Wrappable<EventEmitter> {
+ public:
+  using Listeners = std::vector<v8::Global<v8::Function>>;
+
+  EventEmitter();
+  ~EventEmitter() override;
+
+  static gin::WrapperInfo kWrapperInfo;
+
+  // gin::Wrappable:
+  gin::ObjectTemplateBuilder GetObjectTemplateBuilder(
+      v8::Isolate* isolate) final;
+
+  Listeners* listeners() { return &listeners_; }
+
+ private:
+  // Bound methods for the Event JS object.
+  void AddListener(gin::Arguments* arguments);
+  void RemoveListener(v8::Local<v8::Function> function);
+  bool HasListener(v8::Local<v8::Function> function);
+  bool HasListeners();
+
+  Listeners listeners_;
+
+  DISALLOW_COPY_AND_ASSIGN(EventEmitter);
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_RENDERER_EVENT_EMITTER_H_