Use a joinable background thread instead of worker pool in gin

gin/v8_platform.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 "gin/public/v8_platform.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/message_loop/message_loop_proxy.h"
-#include "base/threading/worker_pool.h"
+#include "base/threading/thread.h"
 #include "gin/per_isolate_data.h"
 
 namespace gin {
 
 namespace {
 
 base::LazyInstance<V8Platform>::Leaky g_v8_platform = LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
 // static
 V8Platform* V8Platform::Get() { return g_v8_platform.Pointer(); }
 
 V8Platform::V8Platform() {}
 
 V8Platform::~V8Platform() {}
 
 void V8Platform::CallOnBackgroundThread(
     v8::Task* task,
     v8::Platform::ExpectedRuntime expected_runtime) {
-  base::WorkerPool::PostTask(
+  if (!background_thread_) {
+    background_thread_.reset(new base::Thread("gin_background"));
+    background_thread_->Start();
+  }
+  background_thread_->message_loop_proxy()->PostTask(
       FROM_HERE,
-      base::Bind(&v8::Task::Run, base::Owned(task)),
-      expected_runtime == v8::Platform::kLongRunningTask);
+      base::Bind(&v8::Task::Run, base::Owned(task)));
 }
 
 void V8Platform::CallOnForegroundThread(v8::Isolate* isolate, v8::Task* task) {
   PerIsolateData::From(isolate)->message_loop_proxy()->PostTask(
       FROM_HERE, base::Bind(&v8::Task::Run, base::Owned(task)));
 }
 
 double V8Platform::MonotonicallyIncreasingTime() {
   return base::TimeTicks::Now().ToInternalValue() /
       static_cast<double>(base::Time::kMicrosecondsPerSecond);
 }
 
 }  // namespace gin