Reland: 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 logging
 import optparse
 import os
 import sys
@@ skipping 30 matching lines @@
     for i in iz.namelist():
       if i.endswith('.dex'):
         oz.writestr(i, iz.read(i))
     os.remove(options.dex_path)
     os.rename(tmp_dex_path, options.dex_path)
 
 
 def DoDex(options, paths, dex_args=None):
   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]
+  # See https://github.com/android/platform_dalvik/commit/dd140a22d for
+  # --num-threads.
+  dex_cmd = [dx_binary, '--num-threads=8', '--dex', '--force-jumbo',
+             '--output', options.dex_path]
   if options.no_locals != '0':
     dex_cmd.append('--no-locals')
 
   if dex_args:
     dex_cmd += dex_args
 
   dex_cmd += paths
 
   record_path = '%s.md5.stamp' % options.dex_path
   md5_check.CallAndRecordIfStale(
@@ skipping 66 matching lines @@
 
   if options.depfile:
     build_utils.WriteDepfile(
         options.depfile,
         paths + build_utils.GetPythonDependencies())
 
 
 
 if __name__ == '__main__':
   sys.exit(main())