Add context menu support (issue #509):

- Add new CefContextMenuHandler, CefContextMenuParams and CefMenuModel classes.
- Add cef_strings.grd and related infrastructure for supporting translation of CEF strings.
- Generate include/cef_pack_resources.h and include/cef_pack_strings.h files at build time that include all IDs used by CEF pack files.

git-svn-id: https://chromiumembedded.googlecode.com/svn/trunk@596 5089003a-bbd8-11dd-ad1f-f1f9622dbc98

tools/make_pack_header.py

@@ -98,7 +98,11 @@ def MakeFile(output, input):
   guard = 'CEF_INCLUDE_'+string.upper(filename.replace('.', '_'))+'_'
   result = result.replace('$GUARD$', guard)
 
-  old_contents = read_file(output)
+  if path_exists(output):
+    old_contents = read_file(output)
+  else:
+    old_contents = ''
+
   if (result != old_contents):
     write_file(output, result)
     sys.stdout.write('File '+output+' updated.\n')