UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36

Steps to reproduce the problem:
1.  build gn standalone "python ./bootstrap/bootstrap.py -s"
2.  see the result.

What is the expected behavior?
to build without errors

What went wrong?
some source file are missing.

the solution is to add the following patch:

diff --git a/bootstrap/bootstrap.py b/bootstrap/bootstrap.py
index 9a3740e..b3927bf 100755
--- a/bootstrap/bootstrap.py
+++ b/bootstrap/bootstrap.py
@@ -429,6 +429,7 @@ def write_gn_ninja(path, root_gen_dir, options):
       'base/run_loop.cc',
       'base/sequence_checker_impl.cc',
       'base/sequenced_task_runner.cc',
+      'base/sequence_token.cc',
       'base/sha1.cc',
       'base/strings/pattern.cc',
       'base/strings/string_number_conversions.cc',
@@ -439,7 +440,7 @@ def write_gn_ninja(path, root_gen_dir, options):
       'base/strings/stringprintf.cc',
       'base/strings/utf_string_conversion_utils.cc',
       'base/strings/utf_string_conversions.cc',
-      'base/synchronization/cancellation_flag.cc',
+      'base/synchronization/atomic_flag.cc',
       'base/synchronization/lock.cc',
       'base/sys_info.cc',
       'base/task_runner.cc',

Did this work before? Yes see my last request of correcting.

Chrome version: 51.0.2704.103  Channel: dev
OS Version: OS X 10.11.6
Flash Version: Shockwave Flash 22.0 r0