[ES6 modules] ModuleTreeLinker::Instantiate shouldn't proceed on invalid context

third_party/WebKit/Source/core/loader/modulescript/ModuleTreeLinker.cpp

 // Copyright 2017 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 "core/loader/modulescript/ModuleTreeLinker.h"
 
 #include "bindings/core/v8/ScriptModule.h"
 #include "core/dom/AncestorList.h"
 #include "core/dom/ModuleScript.h"
 #include "core/loader/modulescript/ModuleScriptFetchRequest.h"
@@ skipping 358 matching lines @@
     Instantiate();
   }
 }
 
 void ModuleTreeLinker::Instantiate() {
   CHECK(module_script_);
   AdvanceState(State::kInstantiating);
 
   // https://html.spec.whatwg.org/multipage/webappapis.html#internal-module-script-graph-fetching-procedure
 
+  // [nospec] Abort the steps if the browsing context is discarded.
+  if (!modulator_->HasValidContext()) {
+    descendants_module_script_ = nullptr;
+    AdvanceState(State::kFinished);
+    return;
+  }
+
   // Step 5. Let instantiationStatus be null.
   // Note: The |error| variable corresponds to spec variable
   // "instantiationStatus". If |error| is empty, it indicates successful
   // completion.
   ScriptValue error;
 
   // Step 6. If result's instantiation state is "errored",...
   if (module_script_->InstantiationState() ==
       ModuleInstantiationState::kErrored) {
     // ... Set instantiationStatus to record.ModuleDeclarationInstantiation().
@@ skipping 123 matching lines @@
   HeapHashSet<Member<ModuleScript>> uninstantiated_set;
   for (const auto& script : inclusive_descendants) {
     if (script->InstantiationState() ==
         ModuleInstantiationState::kUninstantiated)
       uninstantiated_set.insert(script);
   }
   return uninstantiated_set;
 }
 
 }  // namespace blink