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

third_party/WebKit/Source/core/dom/ModulatorImpl.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/dom/ModulatorImpl.h"
 
 #include "core/dom/ExecutionContext.h"
 #include "core/dom/ModuleMap.h"
 #include "core/dom/ModuleScript.h"
 #include "core/dom/ScriptModuleResolverImpl.h"
@@ skipping 93 matching lines @@
   // https://crbug.com/715376
   CHECK(RuntimeEnabledFeatures::moduleScriptsEnabled());
 
   loader_registry_->Fetch(request, level, this, fetcher_.Get(), client);
 }
 
 ModuleScript* ModulatorImpl::GetFetchedModuleScript(const KURL& url) {
   return map_->GetFetchedModuleScript(url);
 }
 
+bool ModulatorImpl::HasValidContext() {
+  return script_state_->ContextIsValid();
+}
+
 ScriptModule ModulatorImpl::CompileModule(
     const String& provided_source,
     const String& url_str,
     AccessControlStatus access_control_status) {
   // Implements Steps 3-6 of
   // https://html.spec.whatwg.org/multipage/webappapis.html#creating-a-module-script
 
   // Step 3. Let realm be the provided environment settings object's Realm.
   // Note: Realm is v8::Context.
 
@@ skipping 90 matching lines @@
   visitor->Trace(loader_registry_);
   visitor->Trace(tree_linker_registry_);
   visitor->Trace(script_module_resolver_);
 }
 
 DEFINE_TRACE_WRAPPERS(ModulatorImpl) {
   visitor->TraceWrappers(map_);
 }
 
 }  // namespace blink