Initialize TaskScheduler before IO thread in service process.

This is needed to migrate net::SerialWorker (used early on the IO
thread) from base::WorkerPool to base::TaskScheduler. Initializing
base::TaskScheduler early matches the behavior of the browser
process.

Bug: 
Change-Id: I0e409980228c379ccabadc3e32f0b9255d91a2e0
Reviewed-on: https://chromium-review.googlesource.com/660598Reviewed-by: Gene Gutnik <gene@chromium.org>
Commit-Queue: Francois Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501251}

chrome/service/service_process.cc

@@ -154,16 +154,6 @@ bool ServiceProcess::Initialize(base::MessageLoopForUI* message_loop,
   main_message_loop_ = message_loop;
   service_process_state_.reset(state);
   network_change_notifier_.reset(net::NetworkChangeNotifier::Create());
-  base::Thread::Options options;
-  options.message_loop_type = base::MessageLoop::TYPE_IO;
-  io_thread_.reset(new ServiceIOThread("ServiceProcess_IO"));
-  file_thread_.reset(new base::Thread("ServiceProcess_File"));
-  if (!io_thread_->StartWithOptions(options) ||
-      !file_thread_->StartWithOptions(options)) {
-    NOTREACHED();
-    Teardown();
-    return false;
-  }
 
   // Initialize TaskScheduler and redirect SequencedWorkerPool tasks to it.
   constexpr int kMaxBackgroundThreads = 1;
@@ -183,6 +173,18 @@ bool ServiceProcess::Initialize(base::MessageLoopForUI* message_loop,
 
   base::SequencedWorkerPool::EnableWithRedirectionToTaskSchedulerForProcess();
 
+  // Initialize the IO and FILE threads.
+  base::Thread::Options options;
+  options.message_loop_type = base::MessageLoop::TYPE_IO;
+  io_thread_.reset(new ServiceIOThread("ServiceProcess_IO"));
+  file_thread_.reset(new base::Thread("ServiceProcess_File"));
+  if (!io_thread_->StartWithOptions(options) ||
+      !file_thread_->StartWithOptions(options)) {
+    NOTREACHED();
+    Teardown();
+    return false;
+  }
+
   // Since SequencedWorkerPool is redirected to TaskScheduler, the value of
   // |kMaxBlockingPoolThreads| is ignored.
   constexpr int kMaxBlockingPoolThreads = 3;