Initialize run_webkit_tests's image-first-tests flag from file

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py

 # Copyright (C) 2010 Google Inc. All rights reserved.
 # Copyright (C) 2010 Gabor Rapcsanyi (rgabor@inf.u-szeged.hu), University of Szeged
 # Copyright (C) 2011 Apple Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
@@ skipping 537 matching lines @@
         options.skipped = 'default'
 
     if not options.total_shards and 'GTEST_TOTAL_SHARDS' in port.host.environ:
         options.total_shards = int(port.host.environ['GTEST_TOTAL_SHARDS'])
     if not options.shard_index and 'GTEST_SHARD_INDEX' in port.host.environ:
         options.shard_index = int(port.host.environ['GTEST_SHARD_INDEX'])
 
     if not options.seed:
         options.seed = port.host.time()
 
+    if not options.image_first_tests:
+        image_first_tests_path = port.host.filesystem.join(port.layout_tests_dir(), 'ImageFirstTests')
+        options.image_first_tests.extend(line for line in open(image_first_tests_path).read().strip().split('\n') if line)

[qyearsley, 2017/03/30 17:26:12]

In general, most of the code in webkitpy interacts with the filesystem
(including reading files) via a FileSystem object so that it can be replaced by
MockFileSystem in unit tests.

So for example, here would want to do something like:
    contents = port.host.filesystem.read_text_file(image_first_tests_path)
    options.image_first_tests.extend(line for line in contents.splitlines(False)
if line)

Note, if there is extra whitespace at the beginning and end of lines (e.g.
"one\n  two \nthree\n") then it'll be kept, but I assume that's OK. If it's not,
then we could change it to:
options.image_first_tests.extend(line.strip() for line in lines if line.strip())

I think it's a good idea to add a simple test for this in
run_webkit_tests_unittest.py.

[Gleb Lanbin, 2017/03/30 23:45:39]

Done.

+
 
 def _run_tests(port, options, args, printer):
     _set_up_derived_options(port, options, args)
     manager = Manager(port, options, printer)
     printer.print_config(port.results_directory())
     return manager.run(args)
 
 
 def run(port, options, args, logging_stream, stdout):
     logger = logging.getLogger()
@@ skipping 27 matching lines @@
             _log.debug('\t%s', process)
 
         return run_details
 
     finally:
         printer.cleanup()
 
 if __name__ == '__main__':
     exit_code = main(sys.argv[1:], sys.stdout, sys.stderr)
     sys.exit(exit_code)