combine base_unittest.py modules from gm and tools

gm/rebaseline_server/imagediffdb.py

Index: gm/rebaseline_server/imagediffdb.py
diff --git a/gm/rebaseline_server/imagediffdb.py b/gm/rebaseline_server/imagediffdb.py
index f6071f9700661abb3d405881e5eba751a2ede7d0..261cad318bc3b9bbbf53909190c94e3b400e3864 100644
--- a/gm/rebaseline_server/imagediffdb.py
+++ b/gm/rebaseline_server/imagediffdb.py
@@ -9,6 +9,7 @@ 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
@@ -19,11 +20,10 @@ 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')