Make skydb --gdb work on mac.

sky/tools/mojo_cache_linker.py

 #!/usr/bin/env python
 # Copyright 2015 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.
 
 import argparse
 import logging
 import os
 import sys
 import subprocess
 import json
+import platform
 
 
 def library_paths(build_dir):
     for name in os.listdir(build_dir):
         path = os.path.realpath(os.path.join(build_dir, name))
         if not os.path.isfile(path):
             continue
 
         # Only include suffixes we care about:
         basename, ext = os.path.splitext(name)
@@ skipping 15 matching lines @@
     except:
         return None
     return cache.get(path)
 
 
 def compute_path_to_app_id_map(paths, cache, cache_mtime):
     path_to_app_id_map = {}
     for path in paths:
         app_id = get_cached_app_id(path, cache, cache_mtime)
         if not app_id:
-            logging.info('sha256sum %s' % path)
+            if platform.system() == 'Darwin':
+                logging.info('shasum -a 256 %s' % path)
+                output = subprocess.check_output(['shasum', '-a', '256', path])
+            else:
+                logging.info('sha256sum %s' % path)
+                output = subprocess.check_output(['sha256sum', path])
             # Example output:
             # f82a3551478a9a0e010adccd675053b9 png_viewer.mojo
-            output = subprocess.check_output(['sha256sum', path])
             app_id = output.strip().split()[0]
         path_to_app_id_map[path] = app_id
     return path_to_app_id_map
 
 
 def read_app_id_cache(cache_path):
     try:
         with open(cache_path, 'r') as cache_file:
             return json.load(cache_file), os.path.getmtime(cache_path)
     except:
@@ skipping 59 matching lines @@
 
         if os.path.lexists(link_path):
             logging.debug('link already exists %s, replacing' % path)
             os.unlink(link_path)
 
         os.symlink(path, link_path)
 
 
 if __name__ == '__main__':
     main()