Reduce overbuilding due to about_credits.html

tools/licenses.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 """Utility for checking and processing licensing information in third_party
 directories.
 
 Usage: licenses.py <command>
 
@@ skipping 567 matching lines @@
 
     entries.sort(key=lambda entry: (entry['name'], entry['content']))
     entries_contents = '\n'.join([entry['content'] for entry in entries])
     file_template = open(file_template_file).read()
     template_contents = "<!-- Generated by licenses.py; do not edit. -->"
     template_contents += EvaluateTemplate(file_template,
                                           {'entries': entries_contents},
                                           escape=False)
 
     if output_file:
-      with open(output_file, 'w') as output:
-        output.write(template_contents)
+      changed = True
+      try:
+        old_output = open(output_file, 'r').read()
+        if old_output == template_contents:
+          changed = False
+      except:
+        pass
+      if changed:
+        with open(output_file, 'w') as output:
+          output.write(template_contents)
     else:
       print template_contents
 
     if depfile:
       assert output_file
       # Add in build.ninja so that the target will be considered dirty whenever
       # gn gen is run. Otherwise, it will fail to notice new files being added.
       # This is still no perfect, as it will fail if no build files are changed,
       # but a new README.chromium / LICENSE is added. This shouldn't happen in
       # practice however.
@@ skipping 31 matching lines @@
                                args.output_file, args.target_os,
                                args.gn_out_dir, args.gn_target, args.depfile):
             return 1
     else:
         print __doc__
         return 1
 
 
 if __name__ == '__main__':
   sys.exit(main())