Add new isolation mode "prepare".

tools/isolate_driver.py

 #!/usr/bin/env python
 # 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.
 
 """Adaptor script called through build/isolate.gypi.
 
 Creates a wrapping .isolate which 'includes' the original one, that can be
 consumed by tools/swarming_client/isolate.py. Path variables are determined
 based on the current working directory. The relative_cwd in the .isolated file
 is determined based on the .isolate file that declare the 'command' variable to
 be used so the wrapping .isolate doesn't affect this value.
 
 This script loads build.ninja and processes it to determine all the executables
 referenced by the isolated target. It adds them in the wrapping .isolate file.
 
 WARNING: The target to use for build.ninja analysis is the base name of the
 .isolate file plus '_run'. For example, 'foo_test.isolate' would have the target
 'foo_test_run' analysed.
 """
 
-import StringIO
 import glob
+import json
 import logging
 import os
 import posixpath
+import StringIO
 import subprocess
 import sys
 import time
 
 TOOLS_DIR = os.path.dirname(os.path.abspath(__file__))
 SWARMING_CLIENT_DIR = os.path.join(TOOLS_DIR, 'swarming_client')
 SRC_DIR = os.path.dirname(TOOLS_DIR)
 
 sys.path.insert(0, SWARMING_CLIENT_DIR)
 
@@ skipping 204 matching lines @@
   out = StringIO.StringIO()
   isolate_format.print_all(comment, isolate_dict, out)
   isolate_content = out.getvalue()
   with open(temp_isolate, 'wb') as f:
     f.write(isolate_content)
   logging.info('Added %d dynamic libs', len(binary_deps))
   logging.debug('%s', isolate_content)
   args[isolate_index] = temp_isolate
 
 
+def prepare_isolate_call(args, output):
+  """Gathers all information required to run isolate.py later.
+
+  Dumps it as JSON to |output| file.
+  """
+  with open(output, 'wb') as f:
+    json.dump({
+      'args': args,
+      'dir': os.getcwd(),
+      'version': 1,
+    }, f, indent=2, sort_keys=True)
+
+
 def main():
   logging.basicConfig(level=logging.ERROR, format='%(levelname)7s %(message)s')
   args = sys.argv[1:]
+  mode = args[0] if args else None
   isolate = None
   isolated = None
   is_component = False
   for i, arg in enumerate(args):
     if arg == '--isolate':
       isolate = i + 1
     if arg == '--isolated':
       isolated = i + 1
     if arg == 'component=shared_library':
       is_component = True
-  if isolate is None or isolated is None:
+  if isolate is None or isolated is None or not mode:
     print >> sys.stderr, 'Internal failure'
     return 1
 
   if is_component:
     create_wrapper(args, isolate, isolated)
 
+  # In 'prepare' mode just collect all required information for postponed
+  # isolated.py invocation later, store it in *.isolated.gen.json file.
+  if mode == 'prepare':
+    prepare_isolate_call(args[1:], args[isolated] + '.gen.json')
+    return 0
+
   swarming_client = os.path.join(SRC_DIR, 'tools', 'swarming_client')
   sys.stdout.flush()
   result = subprocess.call(
       [sys.executable, os.path.join(swarming_client, 'isolate.py')] + args)
   return result
 
 
 if __name__ == '__main__':
   sys.exit(main())