luci-py: Refactor file writing code to allow file objects.

client/run_isolated.py

 #!/usr/bin/env python
 # Copyright 2012 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 """Runs a command with optional isolated input/output.
 
 Despite name "run_isolated", can run a generic non-isolated command specified as
 args.
 
@@ skipping 263 matching lines @@
       storage=storage,
       cache=cache,
       outdir=outdir,
       use_symlinks=use_symlinks)
   return bundle, {
     'duration': time.time() - start,
     'initial_number_items': cache.initial_number_items,
     'initial_size': cache.initial_size,
     'items_cold': base64.b64encode(large.pack(sorted(cache.added))),
     'items_hot': base64.b64encode(
-        large.pack(sorted(set(cache.linked) - set(cache.added)))),
+        large.pack(sorted(set(cache.used) - set(cache.added)))),
   }
 
 
 def delete_and_upload(storage, out_dir, leak_temp_dir):
   """Deletes the temporary run directory and uploads results back.
 
   Returns:
     tuple(outputs_ref, success, stats)
     - outputs_ref: a dict referring to the results archived back to the isolated
           server, if applicable.
@@ skipping 474 matching lines @@
     print >> sys.stderr, ex.message
     return 1
 
 
 if __name__ == '__main__':
   subprocess42.inhibit_os_error_reporting()
   # Ensure that we are always running with the correct encoding.
   fix_encoding.fix_encoding()
   file_path.enable_symlink()
   sys.exit(main(sys.argv[1:]))