grit: Add fallback_to_default_layout attribute to <output>

grit/node/include.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.
 
 """Handling of the <include> element.
 """
 
 import os
 
@@ skipping 50 matching lines @@
     # the path to be relative against our basedir.
     if self.attrs.get('use_base_dir', 'true') != 'true':
       return os.path.relpath(self.attrs['file'], self.GetRoot().GetBaseDir())
 
     return self.attrs['file']
 
   def FileForLanguage(self, lang, output_dir):
     """Returns the file for the specified language.  This allows us to return
     different files for different language variants of the include file.
     """
-    return self.ToRealPath(self.GetInputPath())
+    input_path = self.GetInputPath()
+    if input_path is None:
+      return None
+
+    return self.ToRealPath(input_path)
 
   def GetDataPackPair(self, lang, encoding):
     """Returns a (id, string) pair that represents the resource id and raw
     bytes of the data.  This is used to generate the data pack data file.
     """
     # TODO(benrg/joi): Move this and other implementations of GetDataPackPair
     # to grit.format.data_pack?
     from grit.format import rc_header
     id_map = rc_header.GetIds(self.GetRoot())
     id = id_map[self.GetTextualIds()[0]]
@@ skipping 57 matching lines @@
     node.StartParsing('include', parent)
     node.HandleAttribute('name', name)
     node.HandleAttribute('type', type)
     node.HandleAttribute('file', file)
     node.HandleAttribute('translateable', translateable)
     node.HandleAttribute('filenameonly', filenameonly)
     node.HandleAttribute('mkoutput', mkoutput)
     node.HandleAttribute('relativepath', relativepath)
     node.EndParsing()
     return node