rebaseline.py: fix --add-new when there are no expectations at all

tools/rebaseline.py

 #!/usr/bin/python
 
 '''
 Copyright 2012 Google Inc.
 
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 '''
 
 '''
@@ skipping 286 matching lines @@
 parser = argparse.ArgumentParser()
 parser.add_argument('--actuals-base-url',
                     help='base URL from which to read files containing JSON ' +
                     'summaries of actual GM results; defaults to %(default)s',
                     default='http://skia-autogen.googlecode.com/svn/gm-actual')
 parser.add_argument('--actuals-filename',
                     help='filename (within builder-specific subdirectories ' +
                     'of ACTUALS_BASE_URL) to read a summary of results from; ' +
                     'defaults to %(default)s',
                     default='actual-results.json')
-# TODO(epoger): Add test that exercises --add-new argument.
 parser.add_argument('--add-new', action='store_true',
                     help='in addition to the standard behavior of ' +
                     'updating expectations for failing tests, add ' +
                     'expectations for tests which don\'t have expectations ' +
                     'yet.')
 parser.add_argument('--builders', metavar='BUILDER', nargs='+',
                     help='which platforms to rebaseline; ' +
                     'if unspecified, rebaseline all platforms, same as ' +
                     '"--builders %s"' % ' '.join(sorted(TEST_BUILDERS)))
 # TODO(epoger): Add test that exercises --configs argument.
@@ skipping 59 matching lines @@
         add_new=args.add_new)
     try:
       rebaseliner.RebaselineSubdir(builder=builder)
     except BaseException as e:
       exception_handler.RaiseExceptionOrContinue(e)
   else:
     exception_handler.RaiseExceptionOrContinue(_InternalException(
         'expectations_json_file %s not found' % expectations_json_file))
 
 exception_handler.ReportAllFailures()