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

extensions/renderer/native_handler.cc

 // Copyright 2014 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/native_handler.h"
 
+#include "base/logging.h"
+
 namespace extensions {
 
 NativeHandler::NativeHandler() : is_valid_(true) {}
 
-NativeHandler::~NativeHandler() {}
+NativeHandler::~NativeHandler() {
+  CHECK(!is_valid_) << "NativeHandlers must be invalidated before destruction";
+}
 
-void NativeHandler::Invalidate() { is_valid_ = false; }
+void NativeHandler::Invalidate() {
+  CHECK(is_valid_);
+  is_valid_ = false;
+}
 
 }  // namespace extensions