[libfuzzer] support multiple seed_corpus directories.

testing/libfuzzer/archive_corpus.py

 #!/usr/bin/python2
 #
 # 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.
 
 """Archive corpus file into zip and generate .d depfile.
 
 Invoked by GN from fuzzer_test.gni.
 """
 
 from __future__ import print_function
 import argparse
 import os
 import sys
 import warnings
 import zipfile
 
 
 def main():
   parser = argparse.ArgumentParser(description="Generate fuzzer config.")
-  parser.add_argument('--corpus', required=True)
-  parser.add_argument('--output', required=True)
+  parser.add_argument('corpus_directories', metavar='corpus_dir', type=str,
+                      nargs='+')
+  parser.add_argument('--output', metavar='output_archive_name.zip',
+                      required=True)
   args = parser.parse_args()
 
   corpus_files = []
 
-  for (dirpath, _, filenames) in os.walk(args.corpus):
-    for filename in filenames:
-      full_filename = os.path.join(dirpath, filename)
-      corpus_files.append(full_filename)
+  for directory in args.corpus_directories:
+    for (dirpath, _, filenames) in os.walk(directory):
+      for filename in filenames:
+        full_filename = os.path.join(dirpath, filename)
+        corpus_files.append(full_filename)
 
   with zipfile.ZipFile(args.output, 'w') as z:
     # Turn warnings into errors to interrupt the build: crbug.com/653920.
     with warnings.catch_warnings():
       warnings.simplefilter("error")
       for i, corpus_file in enumerate(corpus_files):
         # To avoid duplication of filenames inside the archive, use numbers.
         arcname = '%016d' % i
         z.write(corpus_file, arcname)
 
 
 if __name__ == '__main__':
   main()