rename rebaseline_server JSON constants to be more consistent

gm/rebaseline_server/imagepairset.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.
 
 ImagePairSet class; see its docstring below.
 """
 
 # System-level imports
 import posixpath
 
 # Local imports
 import column
+import imagepair
 
 # Keys used within dictionary representation of ImagePairSet.
 # NOTE: Keep these in sync with static/constants.js
-KEY__IMAGEPAIRS = 'imagePairs'
-KEY__IMAGESETS = 'imageSets'
+KEY__ROOT__EXTRACOLUMNHEADERS = 'extraColumnHeaders'
+KEY__ROOT__HEADER = 'header'
+KEY__ROOT__IMAGEPAIRS = 'imagePairs'
+KEY__ROOT__IMAGESETS = 'imageSets'
 KEY__IMAGESETS__FIELD__BASE_URL = 'baseUrl'
 KEY__IMAGESETS__FIELD__DESCRIPTION = 'description'
 KEY__IMAGESETS__SET__DIFFS = 'diffs'
 KEY__IMAGESETS__SET__IMAGE_A = 'imageA'
 KEY__IMAGESETS__SET__IMAGE_B = 'imageB'
 KEY__IMAGESETS__SET__WHITEDIFFS = 'whiteDiffs'
 
 DEFAULT_DESCRIPTIONS = ('setA', 'setB')
 
 
@@ skipping 101 matching lines @@
     return asdict
 
   def as_dict(self):
     """Returns a dictionary describing this package of ImagePairs.
 
     Uses the KEY__* constants as keys.
     """
     key_description = KEY__IMAGESETS__FIELD__DESCRIPTION
     key_base_url = KEY__IMAGESETS__FIELD__BASE_URL
     return {
-        column.KEY__EXTRACOLUMNHEADERS: self._column_headers_as_dict(),
-        KEY__IMAGEPAIRS: self._image_pair_dicts,
-        KEY__IMAGESETS: {
+        KEY__ROOT__EXTRACOLUMNHEADERS: self._column_headers_as_dict(),
+        KEY__ROOT__IMAGEPAIRS: self._image_pair_dicts,
+        KEY__ROOT__IMAGESETS: {
             KEY__IMAGESETS__SET__IMAGE_A: {
                 key_description: self._descriptions[0],
                 key_base_url: self._image_base_url,
             },
             KEY__IMAGESETS__SET__IMAGE_B: {
                 key_description: self._descriptions[1],
                 key_base_url: self._image_base_url,
             },
             KEY__IMAGESETS__SET__DIFFS: {
                 key_description: 'color difference per channel',
                 key_base_url: posixpath.join(
                     self._diff_base_url, 'diffs'),
             },
             KEY__IMAGESETS__SET__WHITEDIFFS: {
                 key_description: 'differing pixels in white',
                 key_base_url: posixpath.join(
                     self._diff_base_url, 'whitediffs'),
             },
         },
     }