Move the event attach/detach logic on unload from event.js to

extensions/renderer/native_handler.h

Index: extensions/renderer/native_handler.h
diff --git a/extensions/renderer/native_handler.h b/extensions/renderer/native_handler.h
index c0660c803bd7da71bc9536779c97851145cc8b10..1491feb84c3c703c710bce598dd31356a75d9741 100644
--- a/extensions/renderer/native_handler.h
+++ b/extensions/renderer/native_handler.h
@@ -29,6 +29,9 @@ class NativeHandler {
   //
   // Subclasses should override to invalidate their own V8 state. If they do
   // they must call their superclass' Invalidate().
+  //
+  // Invalidate() will be called on destruction, if it hasn't already been.
+  // Subclasses don't need to do it themselves.
   virtual void Invalidate();
 
  protected: