new tool: download all GM images for a given builder, ready for skdiff

gm/gm_json.py

 #!/usr/bin/env python
 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Schema of the JSON summary file written out by the GM tool.
 
 This must be kept in sync with the kJsonKey_ constants in gm_expectations.cpp !
 """
 
@@ skipping 86 matching lines @@
                       gm_actuals_root_url=GM_ACTUALS_ROOT_HTTP_URL):
   """Return the URL we can use to download a particular version of
   the actually-generated image for this particular GM test.
 
   test_name: name of the test, e.g. 'perlinnoise'
   hash_type: string indicating the hash type used to generate hash_digest,
              e.g. JSONKEY_HASHTYPE_BITMAP_64BITMD5
   hash_digest: the hash digest of the image to retrieve
   gm_actuals_root_url: root url where actual images are stored
   """
+  # TODO(epoger): Maybe use url_or_path.join() so that, for testing, this can
+  # return either a URL or a local filepath?
   return '%s/%s/%s/%s.png' % (gm_actuals_root_url, hash_type, test_name,
                               hash_digest)
 
 def LoadFromString(file_contents):
   """Loads the JSON summary written out by the GM tool.
      Returns a dictionary keyed by the values listed as JSONKEY_ constants
      above."""
   # TODO(epoger): we should add a version number to the JSON file to ensure
   # that the writer and reader agree on the schema (raising an exception
   # otherwise).
   json_dict = json.loads(file_contents)
   return json_dict
 
 def LoadFromFile(file_path):
   """Loads the JSON summary written out by the GM tool.
      Returns a dictionary keyed by the values listed as JSONKEY_ constants
      above."""
   file_contents = open(file_path, 'r').read()
   return LoadFromString(file_contents)
 
 def WriteToFile(json_dict, file_path):
   """Writes the JSON summary in json_dict out to file_path.
 
   The file is written Unix-style (each line ends with just LF, not CRLF);
   see https://code.google.com/p/skia/issues/detail?id=1815 for reasons."""
   with io.open(file_path, mode='w', newline='', encoding='utf-8') as outfile:
     outfile.write(unicode(json.dumps(json_dict, outfile, sort_keys=True,
                                      indent=2)))