Use TaskScheduler instead of WorkerPool in v8_platform.cc.

gin/test/v8_test.h

 // Copyright 2013 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 GIN_TEST_V8_TEST_H_
 #define GIN_TEST_V8_TEST_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
+#include "base/test/scoped_async_task_scheduler.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "v8/include/v8.h"
 
 namespace gin {
 
 class IsolateHolder;
 
 // V8Test is a simple harness for testing interactions with V8. V8Test doesn't
 // have any dependencies on Gin's module system.
 class V8Test : public testing::Test {
  public:
   V8Test();
   ~V8Test() override;
 
   void SetUp() override;
   void TearDown() override;
 
  protected:
   base::MessageLoop message_loop_;
+
+  // Required by gin::V8Platform::CallOnBackgroundThread(). Can't be a
+  // ScopedTaskScheduler because v8 synchronously waits for tasks to run.
+  base::test::ScopedAsyncTaskScheduler scoped_async_task_scheduler_;
+
   std::unique_ptr<IsolateHolder> instance_;
   v8::Persistent<v8::Context> context_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(V8Test);
 };
 
 }  // namespace gin
 
 #endif  // GIN_TEST_V8_TEST_H_