gn: bootstrap: add base/task_scheduler/task_tracker_posix.cc to sources

Review-Url: https://codereview.chromium.org/2480253005
Cr-Original-Commit-Position: refs/heads/master@{#430670}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: aaeeef1bb01f6ff4154652e0999ae4a8834324ca

tools/gn/bootstrap/bootstrap.py

diff --git a/tools/gn/bootstrap/bootstrap.py b/tools/gn/bootstrap/bootstrap.py
index 6059741..78e508d 100755
--- a/tools/gn/bootstrap/bootstrap.py
+++ b/tools/gn/bootstrap/bootstrap.py
@@ -532,6 +532,7 @@
         'base/synchronization/read_write_lock_posix.cc',
         'base/synchronization/waitable_event_posix.cc',
         'base/sys_info_posix.cc',
+        'base/task_scheduler/task_tracker_posix.cc',
         'base/threading/platform_thread_internal_posix.cc',
         'base/threading/platform_thread_posix.cc',
         'base/threading/thread_local_storage_posix.cc',