[Extensions Bindings] Add Events support

extensions/renderer/event_emitter.cc

Index: extensions/renderer/event_emitter.cc
diff --git a/extensions/renderer/event_emitter.cc b/extensions/renderer/event_emitter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b4d34f4f37874a91506c6f1fb95e0a0292bab1ad
--- /dev/null
+++ b/extensions/renderer/event_emitter.cc
@@ -0,0 +1,54 @@
+// 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.
+
+#include "extensions/renderer/event_emitter.h"
+
+#include <algorithm>
+
+#include "gin/object_template_builder.h"
+
+namespace extensions {
+
+gin::WrapperInfo EventEmitter::kWrapperInfo = {gin::kEmbedderNativeGin};
+
+EventEmitter::EventEmitter() {}
+
+EventEmitter::~EventEmitter() {}
+
+gin::ObjectTemplateBuilder EventEmitter::GetObjectTemplateBuilder(
+    v8::Isolate* isolate) {
+  return Wrappable<EventEmitter>::GetObjectTemplateBuilder(isolate)
+      .SetMethod("addListener", &EventEmitter::AddListener)
+      .SetMethod("removeListener", &EventEmitter::RemoveListener)
+      .SetMethod("hasListener", &EventEmitter::HasListener)
+      .SetMethod("hasListeners", &EventEmitter::HasListeners);
+}
+
+void EventEmitter::AddListener(gin::Arguments* arguments) {
+  v8::Local<v8::Function> listener;
+  if (!arguments->GetNext(&listener))
+    return;
+
+  if (!HasListener(listener)) {
+    listeners_.push_back(

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

nit: probably safer to also check that the gin::PerContextData hasn't already
been destroyed (else a listener added here may be able to escape the cleanup
logic above)

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

Done.  It's a tiny shame since EventEmitter otherwise doesn't know it exists on
the PerContextData, but I think that's probably fine.

Right now, I'm getting the context from arguments->holder->CreationContext() -
is that the right way to get the current context?  (Rather than e.g.
arguments->isolate->GetCurrentContext())

[jbroman, 2016/11/04 18:33:04]

Agreed, but that's the cost of relying on the PerContextData to ensure lifetime
correctness here.
arguments->holder->CreationContext() is perfect.

+        v8::Global<v8::Function>(arguments->isolate(), listener));
+  }
+}
+
+void EventEmitter::RemoveListener(v8::Local<v8::Function> listener) {
+  auto iter = std::find(listeners_.begin(), listeners_.end(), listener);
+  if (iter != listeners_.end())
+    listeners_.erase(iter);
+}
+
+bool EventEmitter::HasListener(v8::Local<v8::Function> listener) {
+  return std::find(listeners_.begin(), listeners_.end(), listener) !=
+         listeners_.end();
+}
+
+bool EventEmitter::HasListeners() {
+  return !listeners_.empty();
+}
+
+}  // namespace extensions