Fix issue with doclava download when building varying revisions

build/android/download_doclava.py

 #!/usr/bin/env python
 # Copyright 2016 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.
 
 """Minimal tool to download doclava from Google storage when building for
 Android."""
 
 import os
 import subprocess
 import sys
 
 
 # Its existence signifies an Android checkout.
 ANDROID_ONLY_DIR = os.path.join(os.path.dirname(os.path.abspath(__file__)),
                                 os.pardir, os.pardir,
                                 'third_party', 'android_tools')
 
 
 def main():
   # Some Windows bots inadvertently have third_party/android_tools installed,
   # but are unable to run download_from_google_storage because depot_tools
   # is not in their path, so avoid failure and bail.
   if sys.platform == 'win32':
     return 0
   if not os.path.exists(ANDROID_ONLY_DIR):
     return 0
+  outdir = os.path.join('src', 'buildtools', 'android', 'doclava')
+  tarball = outdir + '.tar.gz'
+  shafile = tarball + '.sha1'
+  # If the expanded directory does not exist, delete the tarball
+  # otherwise if the tarball exists and the SHA1 hash matches,
+  # download_from_google_storage will not download and
+  # extract, and any tools depending on the expanded directory will fail.
+  if os.path.exists(tarball) and not os.path.exists(outdir):
+    os.unlink(tarball)
   subprocess.check_call([
       'download_from_google_storage',
       '--no_resume',
       '--no_auth',
       '--bucket', 'chromium-doclava',
       '--extract',
-      '-s',
-      os.path.join('src', 'buildtools', 'android', 'doclava.tar.gz.sha1')])
+      '-s', shafile])
   return 0
 
 if __name__ == '__main__':
   sys.exit(main())