[Extensions] Handle null ScriptContexts in GetModuleSystem()

extensions/renderer/v8_context_native_handler.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/v8_context_native_handler.h"
 
 #include "base/bind.h"
 #include "extensions/common/features/feature.h"
 #include "extensions/renderer/script_context.h"
 #include "extensions/renderer/script_context_set.h"
@@ skipping 30 matching lines @@
            v8::Integer::New(isolate, availability.result()));
   args.GetReturnValue().Set(ret);
 }
 
 void V8ContextNativeHandler::GetModuleSystem(
     const v8::FunctionCallbackInfo<v8::Value>& args) {
   CHECK_EQ(args.Length(), 1);
   CHECK(args[0]->IsObject());
   ScriptContext* context = ScriptContextSet::GetContextByObject(
       v8::Local<v8::Object>::Cast(args[0]));
-  if (blink::WebFrame::scriptCanAccess(context->web_frame()))
+  if (context && blink::WebFrame::scriptCanAccess(context->web_frame()))
     args.GetReturnValue().Set(context->module_system()->NewInstance());
 }
 
 }  // namespace extensions