[SyncFS] Shutdown LocalFileSyncService before resetting it.

BUG=381050
TEST=./unit_tests --gtest_filter="DriveBackendSyncTest.*" --gtest_repeat=-1 with ASAN build

Review URL: https://codereview.chromium.org/310253005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275411 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/sync_file_system/drive_backend/drive_backend_sync_unittest.cc

@@ -130,7 +130,10 @@ class DriveBackendSyncTest : public testing::Test,
     }
     file_systems_.clear();
 
+    local_sync_service_->Shutdown();
+
     fake_drive_service_helper_.reset();
+    local_sync_service_.reset();
     remote_sync_service_.reset();
 
     content::BrowserThread::GetBlockingPool()->FlushForTesting();