If I touch a file in tools/grit (even the .gni file), some grit unit tests run that fail.

This does not happen on Linux. On Windows I get lots and lots of output that looks like this: 

======================================================================
ERROR: testGenerateDepFile (grit.tool.build_unittest.BuildUnittest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\src\src1\src\tools\grit\grit\tool\build_unittest.py", line 48, in testGenerateDepFile
    '--depfile', expected_dep_file])
  File "D:\src\src1\src\tools\grit\grit\tool\build.py", line 265, in Run
    self.GenerateDepfile(depfile, depdir, first_ids_file, depend_on_stamp)
  File "D:\src\src1\src\tools\grit\grit\tool\build.py", line 511, in GenerateDepfile
    prefix = os.path.relpath(os.getcwd(), depdir)
  File "D:\depot_tools\python276_bin\lib\ntpath.py", line 512, in relpath
    % (path_prefix, start_prefix))
ValueError: path is on drive D:, start on drive c:

======================================================================
ERROR: testGenerateDepFileWithDependOnStamp (grit.tool.build_unittest.BuildUnittest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\src\src1\src\tools\grit\grit\tool\build_unittest.py", line 321, in testGenerateDepFileWithDependOnStamp
    '--depend-on-stamp'])
  File "D:\src\src1\src\tools\grit\grit\tool\build.py", line 265, in Run
    self.GenerateDepfile(depfile, depdir, first_ids_file, depend_on_stamp)
  File "D:\src\src1\src\tools\grit\grit\tool\build.py", line 511, in GenerateDepfile
    prefix = os.path.relpath(os.getcwd(), depdir)
  File "D:\depot_tools\python276_bin\lib\ntpath.py", line 512, in relpath
    % (path_prefix, start_prefix))
ValueError: path is on drive D:, start on drive c:

======================================================================
ERROR: testGenerateDepFileWithResourceIds (grit.tool.build_unittest.BuildUnittest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\src\src1\src\tools\grit\grit\tool\build_unittest.py", line 74, in testGenerateDepFileWithResourceIds
    '--depfile', expected_dep_file])
  File "D:\src\src1\src\tools\grit\grit\tool\build.py", line 265, in Run
    self.GenerateDepfile(depfile, depdir, first_ids_file, depend_on_stamp)
  File "D:\src\src1\src\tools\grit\grit\tool\build.py", line 511, in GenerateDepfile
    prefix = os.path.relpath(os.getcwd(), depdir)
  File "D:\depot_tools\python276_bin\lib\ntpath.py", line 512, in relpath
    % (path_prefix, start_prefix))
ValueError: path is on drive D:, start on drive c: