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

extensions/renderer/script_context.cc

Index: extensions/renderer/script_context.cc
diff --git a/extensions/renderer/script_context.cc b/extensions/renderer/script_context.cc
index c3f04faeada19d37dd1d7d7c1f6bd0455e440186..e5677aadb10597498e0b4d5019bc8cc4d084fd8f 100644
--- a/extensions/renderer/script_context.cc
+++ b/extensions/renderer/script_context.cc
@@ -80,8 +80,7 @@
                              Feature::Context context_type,
                              const Extension* effective_extension,
                              Feature::Context effective_context_type)
-    : is_valid_(true),
-      v8_context_(v8_context->GetIsolate(), v8_context),
+    : v8_context_(v8_context->GetIsolate(), v8_context),
       web_frame_(web_frame),
       extension_(extension),
       context_type_(context_type),
@@ -108,34 +107,17 @@
           << "  extension id: " << GetExtensionID() << "\n"
           << "  effective extension id: "
           << (effective_extension_.get() ? effective_extension_->id() : "");
-  CHECK(!is_valid_) << "ScriptContexts must be invalidated before destruction";
+  Invalidate();
 }
 
 void ScriptContext::Invalidate() {
-  CHECK(is_valid_);
-  is_valid_ = false;
-
-  // TODO(kalman): Make ModuleSystem use AddInvalidationObserver.
-  // Ownership graph is a bit weird here.
+  if (!is_valid())
+    return;
   if (module_system_)
     module_system_->Invalidate();
-
-  // Swap |invalidate_observers_| to a local variable to clear it, and to make
-  // sure it's not mutated as we iterate.
-  std::vector<base::Closure> observers;
-  observers.swap(invalidate_observers_);
-  for (const base::Closure& observer : observers) {
-    observer.Run();
-  }
-  DCHECK(invalidate_observers_.empty())
-      << "Invalidation observers cannot be added during invalidation";
-
+  web_frame_ = NULL;
+  v8_context_.Reset();
   runner_.reset();
-  v8_context_.Reset();
-}
-
-void ScriptContext::AddInvalidationObserver(const base::Closure& observer) {
-  invalidate_observers_.push_back(observer);
 }
 
 const std::string& ScriptContext::GetExtensionID() const {
@@ -162,7 +144,7 @@
   v8::Context::Scope scope(v8_context());
 
   blink::WebScopedMicrotaskSuppression suppression;
-  if (!is_valid_) {
+  if (!is_valid()) {
     return handle_scope.Escape(
         v8::Local<v8::Primitive>(v8::Undefined(isolate())));
   }