[Extensions Bindings] Notify of event unregistration on invalidation

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
index 6705cca8e01438b48c169e2bf43d5742edc62b5d..f160135f1377a57bdacdfaf03af8dd1cc6d9d89a 100644
--- a/extensions/renderer/event_emitter.h
+++ b/extensions/renderer/event_emitter.h
@@ -40,7 +40,11 @@ class EventEmitter final : public gin::Wrappable<EventEmitter> {
   void Fire(v8::Local<v8::Context> context,
             std::vector<v8::Local<v8::Value>>* args);
 
-  Listeners* listeners() { return &listeners_; }
+  // Removes all listeners and marks this object as invalid so that no more
+  // are added.
+  void Invalidate();
+
+  const Listeners* listeners() const { return &listeners_; }
 
  private:
   // Bound methods for the Event JS object.
@@ -50,6 +54,10 @@ class EventEmitter final : public gin::Wrappable<EventEmitter> {
   bool HasListeners();
   void Dispatch(gin::Arguments* arguments);
 
+  // Whether or not this object is still valid; false upon context release.
+  // When invalid, no listeners can be added or removed.
+  bool valid_ = true;
+
   Listeners listeners_;
 
   binding::RunJSFunction run_js_;