Speed up download_android_tools.py by about a third.

tools/android/download_android_tools.py

 #!/usr/bin/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.
 
 """
 Downloads trimmed-down Android Tools from Google Cloud Storage and extracts
 them to INSTALL_DIR, updating INSTALL_DIR/VERSION_* stamp files with current
 version. Does nothing if INSTALL_DIR/VERSION_* are already up to date.
 """
 
+import multiprocessing
 import os
 import shutil
 import subprocess
 import sys
 import tarfile
 
 # Path constants. (All of these should be absolute paths.)
 THIS_DIR = os.path.abspath(os.path.dirname(__file__))
 MOJO_DIR = os.path.abspath(os.path.join(THIS_DIR, '..', '..'))
 # Should be the same as in upload.py.
@@ skipping 55 matching lines @@
 
   # Download tools from GCS.
   archive_path = os.path.join(INSTALL_DIR, tools_name + '.tar.gz')
   download_cmd = ['python', GSUTIL_PATH, 'cp',
                   'gs://mojo/android/tool/%s.tar.gz' % version,
                   archive_path]
   if not RunCommand(download_cmd):
     print ('WARNING: Failed to download Android tools.')
     return
 
-  print "Extracting Android tools (" + tools_name + ")"
-  with tarfile.open(archive_path) as arch:
-    arch.extractall(INSTALL_DIR)
-  os.remove(archive_path)
-  # Write version as the last step.
-  with open(os.path.join(INSTALL_DIR, version_stamp), 'w+') as f:
-    f.write('%s\n' % version)
+  def Extract():
+    print "Extracting Android tools (" + tools_name + ")..."
+    with tarfile.open(archive_path) as arch:
+      arch.extractall(INSTALL_DIR)
+    os.remove(archive_path)
+    # Write version as the last step.
+    with open(os.path.join(INSTALL_DIR, version_stamp), 'w+') as f:
+      f.write('%s\n' % version)
+    print "Finished extracting Android tools (" + tools_name + ")"
+  multiprocessing.Process(target=Extract).start()
 
 def main():
+  UpdateTools('ndk')
   UpdateTools('sdk')
-  UpdateTools('ndk')
 
 if __name__ == '__main__':
   sys.exit(main())