Implement dtrace log parsing for MacOSX.

testing/test_env.py

 #!/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.
 
 """Sets environment variables needed to run a chromium unit test."""
 
 import os
 import subprocess
 import sys
 
 # This is hardcoded to be src/ relative to this script.
 ROOT_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 
 
 def run_executable(cmd, env):
   """Runs an executable with:
     - environment variable CR_SOURCE_ROOT set to the root directory.
     - environment variable LANGUAGE to en_US.UTF-8.
     - Reuses sys.executable automatically.
   """
   # Many tests assume a English interface...
   env['LANGUAGE'] = 'en_US.UTF-8'
   # Used by base/base_paths_linux.cc
   env['CR_SOURCE_ROOT'] = os.path.abspath(ROOT_DIR).encode('utf-8')
   if cmd[0].endswith('.py'):
     cmd.insert(0, sys.executable)
-  return subprocess.call(cmd, env=env)
+  try:
+    return subprocess.call(cmd, env=env)
+  except OSError:
+    print >> sys.stderr, 'Failed to start %s' % cmd
+    raise
 
 
 def main():
   return run_executable(sys.argv[1:], os.environ.copy())
 
 
 if __name__ == "__main__":
   sys.exit(main())