grit: Add fallback_to_default_layout attribute to <output>

grit/format/rc.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.
 
 '''Support for formatting an RC file for compilation.
 '''
 
 import os
 import types
@@ skipping 414 matching lines @@
         ['admin_template', 'chrome_html', 'chrome_scaled_image', 'igoogle',
          'muppet', 'tr_html', 'txt'])
     filename_only = False
     relative_path = False
 
   # By default, we use relative pathnames to included resources so that
   # sharing the resulting .rc files is possible.
   #
   # The FileForLanguage() Function has the side effect of generating the file
   # if needed (e.g. if it is an HTML file include).
-  filename = os.path.abspath(item.FileForLanguage(lang, output_dir))
+  file_for_lang = item.FileForLanguage(lang, output_dir)
+  if file_for_lang is None:
+    return ''
+
+  filename = os.path.abspath(file_for_lang)
   if process_html:
     filename = item.Process(output_dir)
   elif filename_only:
     filename = os.path.basename(filename)
   elif relative_path:
     filename = util.MakeRelativePath(output_dir, filename)
 
   filename = filename.replace('\\', '\\\\')  # escape for the RC format
 
   if isinstance(item, structure.StructureNode) and item.IsExcludedFromRc():
@@ skipping 22 matching lines @@
   'muppet'              : partial(FormatInclude, type='XML'),
   'tr_html'             : partial(FormatInclude, type='HTML'),
   'txt'                 : partial(FormatInclude, type='TXT'),
   'policy_template_metafile': _DoNotFormat,
 }
 
 
 def FormatStructure(item, lang, output_dir):
   formatter = _STRUCTURE_FORMATTERS[item.attrs['type']]
   return formatter(item, lang, output_dir)