Follow-up to crrev.com/583793002 -- check if goma_dir is None.

tools/auto_bisect/builder.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Classes and functions for building Chrome.
 
 This includes functions for running commands to build, as well as
 specific rules about which targets to build.
 """
 
@@ skipping 21 matching lines @@
     """
     if bisect_utils.IsWindowsHost():
       if not opts.build_preference:
         opts.build_preference = 'msvs'
 
       if opts.build_preference == 'msvs':
         if not os.getenv('VS100COMNTOOLS'):
           raise RuntimeError(
               'Path to visual studio could not be determined.')
       else:
+        # Need to re-escape goma dir, see crbug.com/394990.
+        if opts.goma_dir:
+          opts.goma_dir = opts.goma_dir.encode('string_escape')
         SetBuildSystemDefault(opts.build_preference, opts.use_goma,
-                              # Need to re-escape goma dir, see crbug.com/394990
-                              opts.goma_dir.encode('string_escape'))
+                              opts.goma_dir)
     else:
       if not opts.build_preference:
         if 'ninja' in os.getenv('GYP_GENERATORS', default=''):
           opts.build_preference = 'ninja'
         else:
           opts.build_preference = 'make'
 
       SetBuildSystemDefault(opts.build_preference, opts.use_goma, opts.goma_dir)
 
     if not SetupPlatformBuildEnvironment(opts):
@@ skipping 393 matching lines @@
   # (See http://crrev.com/170273005). So, we set this variable explicitly here
   # in order to build Chrome on Android.
   if 'GYP_DEFINES' not in os.environ:
     os.environ['GYP_DEFINES'] = 'OS=android'
   else:
     os.environ['GYP_DEFINES'] += ' OS=android'
 
   if opts.use_goma:
     os.environ['GYP_DEFINES'] += ' use_goma=1'
   return not proc.returncode