rebaseline_server: if creating brand new expectations files, include the header

gm/rebaseline_server/writable_expectations.py

 #!/usr/bin/python
 
 """
 Copyright 2014 Google Inc.
 
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 
 Expectations on local disk that we can modify.
 """
@@ skipping 61 matching lines @@
       modifications: data[KEY__LIVE_EDITS__MODIFICATIONS] coming back from the
           rebaseline_server UI frontend
     """
     logging.info('Reading in dicts from writable Skia checkout in %s ...' %
                  self.root)
     dicts = results.BaseComparisons.read_dicts_from_root(self.root)
 
     # Make sure we have expected-results sections in all our output dicts.
     for pathname, adict in dicts.iteritems():
       if not adict:
-        adict = {}
+        adict = {
+          # TODO(stephana): These values should be defined as constants
+          # somewhere, to be kept in sync between this file and
+          # compare_rendered_pictures.py.
+          gm_json.JSONKEY_HEADER: {
+            gm_json.JSONKEY_HEADER_TYPE: 'ChecksummedImages',
+            gm_json.JSONKEY_HEADER_REVISION: 1,
+          }
+        }
       if not adict.get(gm_json.JSONKEY_EXPECTEDRESULTS, None):
         adict[gm_json.JSONKEY_EXPECTEDRESULTS] = {}
       dicts[pathname] = adict
 
     for modification in modifications:
       expectations = modification[imagepair.KEY__IMAGEPAIRS__EXPECTATIONS]
       _add_image_info_to_expectations(
           expectations=expectations,
           filepath=modification[imagepair.KEY__IMAGEPAIRS__IMAGE_B_URL])
       extra_columns = modification[imagepair.KEY__IMAGEPAIRS__EXTRACOLUMNS]
@@ skipping 73 matching lines @@
   be true.
 
   Args:
     expectations: the expectations dict to augment
     filepath: relative path to the image file
   """
   (checksum_algorithm, checksum_value) = FILEPATH_RE.match(filepath).groups()
   expectations[gm_json.JSONKEY_IMAGE_CHECKSUMALGORITHM] = checksum_algorithm
   expectations[gm_json.JSONKEY_IMAGE_CHECKSUMVALUE] = checksum_value
   expectations[gm_json.JSONKEY_IMAGE_FILEPATH] = filepath