Fix running 'import run_isolated' at python interactive prompt.

run_isolated.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.
 
 """Reads a .isolated, creates a tree of hardlinks and runs the test.
 
 Keeps a local cache.
 """
 
@@ skipping 21 matching lines @@
 import isolateserver
 
 
 # Absolute path to this file (can be None if running from zip on Mac).
 THIS_FILE_PATH = os.path.abspath(__file__) if __file__ else None
 
 # Directory that contains this file (might be inside zip package).
 BASE_DIR = os.path.dirname(THIS_FILE_PATH) if __file__ else None
 
 # Directory that contains currently running script file.
-MAIN_DIR = os.path.dirname(os.path.abspath(zip_package.get_main_script_path()))
+if zip_package.get_main_script_path():
+  MAIN_DIR = os.path.dirname(
+      os.path.abspath(zip_package.get_main_script_path()))
+else:
+  # This happens when 'import run_isolated' is executed at the python
+  # interactive prompt, in that case __file__ is undefined.
+  MAIN_DIR = None
 
 # Types of action accepted by link_file().
 HARDLINK, HARDLINK_WITH_FALLBACK, SYMLINK, COPY = range(1, 5)
 
 # The name of the log file to use.
 RUN_ISOLATED_LOG_FILE = 'run_isolated.log'
 
 # The name of the log to use for the run_test_cases.py command
 RUN_TEST_CASES_LOG = 'run_test_cases.log'
 
@@ skipping 454 matching lines @@
     if settings.read_only:
       logging.info('Making files read only')
       make_writable(outdir, True)
     cwd = os.path.normpath(os.path.join(outdir, settings.relative_cwd))
     logging.info('Running %s, cwd=%s' % (settings.command, cwd))
 
     # TODO(csharp): This should be specified somewhere else.
     # TODO(vadimsh): Pass it via 'env_vars' in manifest.
     # Add a rotating log file if one doesn't already exist.
     env = os.environ.copy()
-    env.setdefault('RUN_TEST_CASES_LOG_FILE',
-                  os.path.join(MAIN_DIR, RUN_TEST_CASES_LOG))
+    if MAIN_DIR:
+      env.setdefault('RUN_TEST_CASES_LOG_FILE',
+                    os.path.join(MAIN_DIR, RUN_TEST_CASES_LOG))
     try:
       with tools.Profiler('RunTest'):
         return subprocess.call(settings.command, cwd=cwd, env=env)
     except OSError:
       print >> sys.stderr, 'Failed to run %s; cwd=%s' % (settings.command, cwd)
       return 1
   finally:
     if outdir:
       rmtree(outdir)
 
@@ skipping 77 matching lines @@
   except Exception, e:
     # Make sure any exception is logged.
     logging.exception(e)
     return 1
 
 
 if __name__ == '__main__':
   # Ensure that we are always running with the correct encoding.
   fix_encoding.fix_encoding()
   sys.exit(main())