Print detailed info in check_gn_headers.py

testing/scripts/check_gn_headers.py

 #!/usr/bin/env python
 # Copyright 2017 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import json
 import os
 import sys
 
 
 import common
 
 
 def main_run(args):
   with common.temporary_file() as tempfile_path:
     rc = common.run_command([
         sys.executable,
         os.path.join(common.SRC_DIR, 'build', 'check_gn_headers.py'),
         '--out-dir',
         os.path.join(args.paths['checkout'], 'out', args.build_config_fs),
         '--whitelist',
         os.path.join(common.SRC_DIR, 'build', 'check_gn_headers_whitelist.txt'),
-        '--json', tempfile_path
+        '--json', tempfile_path,
+        '--verbose',
     ], cwd=common.SRC_DIR)
 
     with open(tempfile_path) as f:
       failures = json.load(f)
 
   json.dump({
       'valid': True,
       'failures': failures,
   }, args.output)
 
   return rc
 
 
 def main_compile_targets(args):
   json.dump([], args.output)
 
 
 if __name__ == '__main__':
   funcs = {
     'run': main_run,
     'compile_targets': main_compile_targets,
   }
   sys.exit(common.run_script(sys.argv[1:], funcs))