[Extensions Bindings] Add Events support

extensions/renderer/api_event_handler.h

+// 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_API_EVENT_HANDLER_H_
+#define EXTENSIONS_RENDERER_API_EVENT_HANDLER_H_
+
+#include <string>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "extensions/renderer/api_binding_types.h"
+#include "extensions/renderer/event_emitter.h"

[jbroman, 2016/11/03 19:28:04]

super-nit: unused include; move to .cc?

[Devlin, 2016/11/04 17:59:30]

Done.

+#include "v8/include/v8.h"
+
+namespace base {
+class ListValue;
+}
+
+namespace gin {
+class Arguments;

[jbroman, 2016/11/03 19:28:04]

nit: unused forward declaration (apologies for missing this earlier)

[Devlin, 2016/11/04 17:59:30]

Done.

+}
+
+namespace extensions {
+
+// The object to handle API events. This includes vending v8::Objects for the
+// event; handling adding, removing, and querying listeners; and firing events
+// to subscribed listeners. Designed to be used across JS contexts, but on a
+// single thread.
+class APIEventHandler {
+ public:
+  APIEventHandler(const binding::RunJSFunction& call_js);
+  ~APIEventHandler();
+
+  // Returns a new v8::Object for an event with the given |event_name|.
+  v8::Local<v8::Object> CreateEventInstance(const std::string& event_name,
+                                            v8::Local<v8::Context> context);
+
+  // Notifies all listeners of the event with the given |event_name| in the
+  // specified |context|, sending the included |arguments|.
+  void FireEventInContext(const std::string& event_name,
+                          v8::Local<v8::Context> context,
+                          const base::ListValue& arguments);
+
+  // Returns the EventListeners for a given |event_name| and |context|.
+  size_t GetNumEventListenersForTesting(const std::string& event_name,
+                                        v8::Local<v8::Context> context);
+
+ private:
+  // Method to run a given v8::Function. Curried in for testing.
+  binding::RunJSFunction call_js_;
+
+  DISALLOW_COPY_AND_ASSIGN(APIEventHandler);
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_RENDERER_API_EVENT_HANDLER_H_