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

extensions/renderer/module_system_test.cc

Index: extensions/renderer/module_system_test.cc
diff --git a/extensions/renderer/module_system_test.cc b/extensions/renderer/module_system_test.cc
index b9d4a4d8f3a31e36ee89e803755a34f75d3a5e03..cc4cbfbaed05f09498bc5a19712092275252a215 100644
--- a/extensions/renderer/module_system_test.cc
+++ b/extensions/renderer/module_system_test.cc
@@ -157,7 +157,7 @@ ModuleSystemTestEnvironment::ModuleSystemTestEnvironment(v8::Isolate* isolate)
 
 ModuleSystemTestEnvironment::~ModuleSystemTestEnvironment() {
   if (context_->is_valid())
-    context_->v8_context()->Exit();
+    ShutdownModuleSystem();
 }
 
 void ModuleSystemTestEnvironment::RegisterModule(const std::string& name,
@@ -196,6 +196,7 @@ void ModuleSystemTestEnvironment::ShutdownGin() {
 }
 
 void ModuleSystemTestEnvironment::ShutdownModuleSystem() {
+  CHECK(context_->is_valid());
   context_->v8_context()->Exit();
   context_->Invalidate();
 }