add --descriptions flag to render_pictures tool

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 30 matching lines @@
 # we haven't had a chance to check in expectations for yet, or we may have
 # consciously decided to leave them without expectations because we are unhappy
 # with the results (although we should try to move away from that, and instead
 # check in expectations with the IGNOREFAILURE flag set).
 JSONKEY_ACTUALRESULTS_NOCOMPARISON = 'no-comparison'
 
 # Tests whose results matched their expectations.
 JSONKEY_ACTUALRESULTS_SUCCEEDED = 'succeeded'
 
 
+# Descriptions of the result set as a whole.
+JSONKEY_DESCRIPTIONS = 'descriptions'
+
+
 JSONKEY_EXPECTEDRESULTS = 'expected-results'
 
 # One or more [HashType/DigestValue] pairs representing valid results for this
 # test.  Typically, there will just be one pair, but we allow for multiple
 # expectations, and the test will pass if any one of them is matched.
 JSONKEY_EXPECTEDRESULTS_ALLOWEDDIGESTS = 'allowed-digests'
 
 # Optional: one or more integers listing Skia bugs (under
 # https://code.google.com/p/skia/issues/list ) that pertain to this expectation.
 JSONKEY_EXPECTEDRESULTS_BUGS = 'bugs'
@@ skipping 120 matching lines @@
 
 
 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)))