Use --num-thread=10 when dexing Android code (saves 5 seconds)

build/android/gyp/dex.py

 #!/usr/bin/env python
 #
 # Copyright 2013 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 optparse
 import os
 import sys
 
 from util import build_utils
 from util import md5_check
 
 
 def DoDex(options, paths):
   dx_binary = os.path.join(options.android_sdk_tools, 'dx')
   # See http://crbug.com/272064 for context on --force-jumbo.
-  dex_cmd = [dx_binary, '--dex', '--force-jumbo', '--output', options.dex_path]
+  # --num-threads=10 made final dexing go from 10s -> 5s on a z620.
+  dex_cmd = [dx_binary, '--num-threads=10', '--dex', '--force-jumbo',
+             '--output', options.dex_path]
   if options.no_locals != '0':
     dex_cmd.append('--no-locals')
 
   dex_cmd += paths
 
   record_path = '%s.md5.stamp' % options.dex_path
   md5_check.CallAndRecordIfStale(
       lambda: build_utils.CheckOutput(dex_cmd, print_stderr=False),
       record_path=record_path,
       input_paths=paths,
@@ skipping 44 matching lines @@
 
   if options.depfile:
     build_utils.WriteDepfile(
         options.depfile,
         paths + build_utils.GetPythonDependencies())
 
 
 
 if __name__ == '__main__':
   sys.exit(main())