svndiff.py: add ability to compare before-and-after JSON files, not just raw images

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 !
 """
 
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 # expectations, and the test will pass if any one of them is matched.
 JSONKEY_EXPECTEDRESULTS_ALLOWEDDIGESTS = 'allowed-digests'
 # If IGNOREFAILURE is set to True, a failure of this test will be reported
 # within the FAILUREIGNORED section (thus NOT causing the buildbots to go red)
 # rather than the FAILED section (which WOULD cause the buildbots to go red).
 JSONKEY_EXPECTEDRESULTS_IGNOREFAILURE = 'ignore-failure'
 
 # Allowed hash types for test expectations.
 JSONKEY_HASHTYPE_BITMAP_64BITMD5 = 'bitmap-64bitMD5'
 
+# Root directory where the buildbots store their actually-generated images...
+#  as a publicly readable HTTP URL:
+GM_ACTUALS_ROOT_HTTP_URL = (
+    'http://chromium-skia-gm.commondatastorage.googleapis.com/gm')
+#  as a GS URL that allows credential-protected write access:
+GM_ACTUALS_ROOT_GS_URL = 'gs://chromium-skia-gm/gm'
+
+# Pattern used to assemble each image's filename
+IMAGE_FILENAME_PATTERN = '(\S+)_(\S+).png'  # matches (testname, config)
+
+def CreateGmActualUrl(test_name, hash_type, hash_digest,
+                      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
+  """
+  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."""
   with open(file_path, 'w') as outfile:
     json.dump(json_dict, outfile, sort_keys=True, indent=2)