Add UTF-8 BOM for chrome_messages_json formatter.

grit/tool/build.py

Index: grit/tool/build.py
diff --git a/grit/tool/build.py b/grit/tool/build.py
index dd0a129978878a076c1a7d7112d53f1f862be4cb..0f2a51eba12391625c57205edff2ac4f415cc0f3 100644
--- a/grit/tool/build.py
+++ b/grit/tool/build.py
@@ -228,9 +228,11 @@ are exported to translation interchange files (e.g. XMB files), etc.
           'resource_map_source', 'resource_file_map_source'):
         encoding = 'cp1252'
       elif output.GetType() in ('android', 'c_format', 'js_map_format', 'plist',
-                                'plist_strings', 'doc', 'json',
-                                'chrome_messages_json'):
+                                'plist_strings', 'doc', 'json'):
         encoding = 'utf_8'
+      elif output.GetType() in ('chrome_messages_json'):
+        # Chrome Web Store currently expects BOM for UTF-8 files :-(
+        encoding = 'utf-8-sig'
       else:
         # TODO(gfeher) modify here to set utf-8 encoding for admx/adml
         encoding = 'utf_16'