Allow the IPC fuzzer to use a platform-specific corpus.

tools/ipc_fuzzer/scripts/ipc_fuzzer_mut.py

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 """Mutational ClusterFuzz fuzzer. A pre-built corpus of ipcdump files has
 to be uploaded to ClusterFuzz along with this script. As chrome is being
 developed, the corpus will become out-of-date and needs to be updated.
 
 This fuzzer will pick some ipcdumps from the corpus, concatenate them with
@@ skipping 23 matching lines @@
     self.ipc_fuzzer_binary = utils.get_fuzzer_application_name()
     self.ipc_replay_binary = utils.get_replay_application_name()
     self.ipc_message_util_binary_path = os.path.join(
         chrome_application_directory, self.ipc_message_util_binary)
     self.ipc_fuzzer_binary_path = os.path.join(
         chrome_application_directory, self.ipc_fuzzer_binary)
     self.ipc_replay_binary_path = os.path.join(
         chrome_application_directory, self.ipc_replay_binary)
 
   def set_corpus(self):
-    input_directory = self.args.input_dir
-    entries = os.listdir(input_directory)
+    # Corpus should be set per job as a fuzzer-specific environment variable.
+    corpus = os.getenv('IPC_CORPUS_DIR', 'default')
+    corpus_directory = os.path.join(self.args.input_dir, corpus)
+    if not os.path.exists(corpus_directory):
+      sys.exit('Corpus directory "%s" not found.' % corpus_directory)
+
+    entries = os.listdir(corpus_directory)
     entries = [i for i in entries if i.endswith(utils.IPCDUMP_EXTENSION)]
-    self.corpus = [os.path.join(input_directory, entry) for entry in entries]
+    self.corpus = [os.path.join(corpus_directory, entry) for entry in entries]
 
   def create_mutated_ipcdump_testcase(self):
     ipcdumps = ','.join(random.sample(self.corpus, IPCDUMP_MERGE_LIMIT))
     tmp_ipcdump_testcase = utils.create_temp_file()
     mutated_ipcdump_testcase = (
         utils.random_ipcdump_testcase_path(self.args.output_dir))
 
     # Concatenate ipcdumps -> tmp_ipcdump.
     cmd = [
       self.ipc_message_util_binary_path,
@@ skipping 22 matching lines @@
     self.set_application_paths()
     self.set_corpus()
     for _ in xrange(self.args.no_of_files):
       self.create_mutated_ipcdump_testcase()
 
     return 0
 
 if __name__ == "__main__":
   fuzzer = MutationalFuzzer()
   sys.exit(fuzzer.main())