Get run_test_cases.py to fail if it fails to get the list of tests it should run.

tools/isolate/data/gtest_fake/gtest_fake_error.py

Index: tools/isolate/data/gtest_fake/gtest_fake_error.py
diff --git a/tools/isolate/data/gtest_fake/gtest_fake_error.py b/tools/isolate/data/gtest_fake/gtest_fake_error.py
new file mode 100755
index 0000000000000000000000000000000000000000..73a7cb5559b65fd983d9276493b4a33d4e356411
--- /dev/null
+++ b/tools/isolate/data/gtest_fake/gtest_fake_error.py
@@ -0,0 +1,32 @@
+#!/usr/bin/env python
+# Copyright (c) 2012 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.
+
+"""Simulate a google-test executable that has an error when listing tests.
+
+http://code.google.com/p/googletest/
+"""
+
+import optparse
+import sys
+
+
+def main():
+  parser = optparse.OptionParser()
+  parser.add_option('--gtest_list_tests', action='store_true')
+  parser.add_option('--gtest_filter')
+  options, args = parser.parse_args()
+  if args:
+    parser.error('Failed to process args %s' % args)
+
+  if options.gtest_list_tests:
+    sys.stderr.write('Unable to list tests')
+    return 1
+
+  sys.stderr.write('Unable to run tests')
+  return 1
+
+
+if __name__ == '__main__':
+  sys.exit(main())