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

extensions/renderer/module_system.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/module_system.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
+#include "base/logging.h"
 #include "base/stl_util.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/trace_event/trace_event.h"
 #include "content/public/renderer/render_frame.h"
 #include "content/public/renderer/render_view.h"
 #include "extensions/common/extension.h"
 #include "extensions/common/extensions_client.h"
 #include "extensions/renderer/console.h"
 #include "extensions/renderer/safe_builtins.h"
@@ skipping 125 matching lines @@
   global->SetHiddenValue(v8::String::NewFromUtf8(isolate, kModuleSystem),
                          v8::External::New(isolate, this));
 
   gin::ModuleRegistry::From(context->v8_context())->AddObserver(this);
   if (context_->GetRenderFrame()) {
     context_->GetRenderFrame()->EnsureMojoBuiltinsAreAvailable(
         context->isolate(), context->v8_context());
   }
 }
 
-ModuleSystem::~ModuleSystem() { Invalidate(); }
+ModuleSystem::~ModuleSystem() {
+}
 
 void ModuleSystem::Invalidate() {
-  if (!is_valid())
-    return;
+  CHECK(is_valid());

[Devlin, 2015/04/10 18:10:40]

It's a little odd that each subclass is expected to CHECK(is_valid()) here. 
Can't we just CHECK it in NativeHandler, since each subclass is already expected
to call it's super?

[not at google - send to devlin, 2015/04/10 18:39:01]

Done.

 
   // Clear the module system properties from the global context. It's polite,
   // and we use this as a signal in lazy handlers that we no longer exist.
   {
     v8::HandleScope scope(GetIsolate());
     v8::Handle<v8::Object> global = context()->v8_context()->Global();
     global->DeleteHiddenValue(
         v8::String::NewFromUtf8(GetIsolate(), kModulesField));
     global->DeleteHiddenValue(
         v8::String::NewFromUtf8(GetIsolate(), kModuleSystem));
@@ skipping 510 matching lines @@
     v8::Handle<v8::Value> value) {
   if (!is_valid())
     return;
   v8::HandleScope handle_scope(GetIsolate());
   v8::Handle<v8::Promise::Resolver> resolver_local(
       v8::Local<v8::Promise::Resolver>::New(GetIsolate(), *resolver));
   resolver_local->Resolve(value);
 }
 
 }  // namespace extensions