Document how to get a specific revision when rebaselining.

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 326 matching lines @@
 
 # main...
 
 parser = argparse.ArgumentParser(
     formatter_class=argparse.RawDescriptionHelpFormatter,
     epilog='Here is the full set of builders we know about:' +
            '\n    '.join([''] + sorted(TEST_BUILDERS)))
 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)s. To get a specific revision (useful for'
+                          'trybots) replace "svn" with "svn-history/r123".'),
                     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')
 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 '
@@ skipping 91 matching lines @@
     except:
       exception_handler.RaiseExceptionOrContinue()
   else:
     try:
       raise _InternalException('expectations_json_file %s not found' %
                                expectations_json_file)
     except:
       exception_handler.RaiseExceptionOrContinue()
 
 exception_handler.ReportAllFailures()