Add ability to output ImageBaseGSUrl to render_picture and use in rebaseline server

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 76 matching lines @@
 
 JSONKEY_HEADER = 'header'
 JSONKEY_HEADER_TYPE = 'type'
 JSONKEY_HEADER_REVISION = 'revision'
 JSONKEY_IMAGE_CHECKSUMALGORITHM = 'checksumAlgorithm'
 JSONKEY_IMAGE_CHECKSUMVALUE = 'checksumValue'
 JSONKEY_IMAGE_COMPARISONRESULT = 'comparisonResult'
 JSONKEY_IMAGE_FILEPATH = 'filepath'
 JSONKEY_SOURCE_TILEDIMAGES = 'tiled-images'
 JSONKEY_SOURCE_WHOLEIMAGE = 'whole-image'
+JSONKEY_IMAGE_BASE_GS_URL = 'image-base-gs-url'
 
 
 # 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'
 
 # Root directory where buildbots store skimage actual results json files.
@@ skipping 82 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)))