combine base_unittest.py modules from gm and tools

gm/rebaseline_server/imagediffdb.py

 #!/usr/bin/python
 
 """
 Copyright 2013 Google Inc.
 
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 
 Calulate differences between image pairs, and store them in a database.
 """
 
+# System-level imports
 import contextlib
 import json
 import logging
 import os
 import re
 import shutil
-import sys
 import tempfile
 import urllib
 
-# Set the PYTHONPATH to include the tools directory.
-sys.path.append(
-    os.path.join(
-        os.path.dirname(os.path.realpath(__file__)), os.pardir, os.pardir,
-                        'tools'))
+# Must fix up PYTHONPATH before importing from within Skia
+import fix_pythonpath  # pylint: disable=W0611
+
+# Imports from within Skia
 import find_run_binary
 
 SKPDIFF_BINARY = find_run_binary.find_path_to_program('skpdiff')
 
 DEFAULT_IMAGE_SUFFIX = '.png'
 DEFAULT_IMAGES_SUBDIR = 'images'
 
 DISALLOWED_FILEPATH_CHAR_REGEX = re.compile('[^\w\-]')
 
 RGBDIFFS_SUBDIR = 'diffs'
@@ skipping 293 matching lines @@
 
   Args:
     expected_image_locator: locator string pointing at expected image
     actual_image_locator: locator string pointing at actual image
 
   Returns: already-sanitized locator where the diffs between expected and
       actual images can be found
   """
   return "%s-vs-%s" % (_sanitize_locator(expected_image_locator),
                        _sanitize_locator(actual_image_locator))