Add ScopedTaskEnvironment in extensions::ModuleSystemTest.

extensions/renderer/module_system_test.h

 // 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.
 
 #ifndef EXTENSIONS_RENDERER_MODULE_SYSTEM_TEST_H_
 #define EXTENSIONS_RENDERER_MODULE_SYSTEM_TEST_H_
 
 #include "base/macros.h"
+#include "base/test/scoped_task_environment.h"
 #include "extensions/renderer/module_system.h"
 #include "extensions/renderer/script_context.h"
 #include "gin/public/context_holder.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "v8/include/v8.h"
 
 namespace extensions {
 class StringSourceMap;
 
 class ModuleSystemTestEnvironment {
@@ skipping 72 matching lines @@
 
   // Make the test fail if any asserts are called. By default a test will fail
   // if no asserts are called.
   void ExpectNoAssertionsMade();
 
   // Runs promises that have been resolved. Resolved promises will not run
   // until this is called.
   void RunResolvedPromises();
 
  private:
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   v8::Isolate* isolate_;
   std::unique_ptr<ModuleSystemTestEnvironment> env_;
   bool should_assertions_be_made_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ModuleSystemTest);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_MODULE_SYSTEM_TEST_H_