[Sync] Move sync thread ownership to ProfileSyncService.

components/sync/driver/glue/sync_backend_host_impl_unittest.cc

Index: components/sync/driver/glue/sync_backend_host_impl_unittest.cc
diff --git a/components/sync/driver/glue/sync_backend_host_impl_unittest.cc b/components/sync/driver/glue/sync_backend_host_impl_unittest.cc
index 935e79fc95ff2514ca670e1be70cb74116743330..56c75fe0a1dbab7b652032152ecee0f07390cbd7 100644
--- a/components/sync/driver/glue/sync_backend_host_impl_unittest.cc
+++ b/components/sync/driver/glue/sync_backend_host_impl_unittest.cc
@@ -154,7 +154,8 @@ class BackendSyncClient : public FakeSyncClient {
 
 class SyncBackendHostTest : public testing::Test {
  protected:
-  SyncBackendHostTest() : fake_manager_(nullptr) {}
+  SyncBackendHostTest()
+      : sync_thread_("SyncThreadForTest"), fake_manager_(nullptr) {}
 
   ~SyncBackendHostTest() override {}
 
@@ -164,6 +165,7 @@ class SyncBackendHostTest : public testing::Test {
     SyncPrefs::RegisterProfilePrefs(pref_service_.registry());
 
     sync_prefs_ = base::MakeUnique<SyncPrefs>(&pref_service_);
+    sync_thread_.StartAndWaitForTesting();
     backend_ = base::MakeUnique<SyncBackendHostImpl>(
         "dummyDebugName", &sync_client_, base::ThreadTaskRunnerHandle::Get(),
         nullptr, sync_prefs_->AsWeakPtr(),
@@ -211,8 +213,7 @@ class SyncBackendHostTest : public testing::Test {
                        base::Unretained(network_resources_.get()), nullptr,
                        base::Bind(&EmptyNetworkTimeUpdate));
     backend_->Initialize(
-        &mock_frontend_, std::unique_ptr<base::Thread>(),
-        base::ThreadTaskRunnerHandle::Get(),
+        &mock_frontend_, &sync_thread_, base::ThreadTaskRunnerHandle::Get(),
         base::ThreadTaskRunnerHandle::Get(), WeakHandle<JsEventHandler>(),
         GURL(std::string()), std::string(), credentials_, true, false,
         base::FilePath(), std::move(fake_manager_factory_),
@@ -267,6 +268,7 @@ class SyncBackendHostTest : public testing::Test {
   base::MessageLoop message_loop_;
   base::ScopedTempDir temp_dir_;
   sync_preferences::TestingPrefServiceSyncable pref_service_;
+  base::Thread sync_thread_;
   StrictMock<MockSyncFrontend> mock_frontend_;
   SyncCredentials credentials_;
   BackendSyncClient sync_client_;