Fix gn bootstrap

R=dpranke

Change-Id: I880c2cc2a2702db6ebbbd90120753587971bb2be
Reviewed-on: https://chromium-review.googlesource.com/1067581Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560326}

tools/gn/bootstrap/bootstrap.py

@@ -600,6 +600,7 @@ def write_gn_ninja(path, root_gen_dir, options, windows_x64_toolchain):
       'base/task_scheduler/scoped_set_task_priority_for_current_thread.cc',
       'base/task_scheduler/sequence.cc',
       'base/task_scheduler/sequence_sort_key.cc',
+      'base/task_scheduler/service_thread.cc',
       'base/task_scheduler/task.cc',
       'base/task_scheduler/task_scheduler.cc',
       'base/task_scheduler/task_scheduler_impl.cc',