* make RunTest's multiprocessing.Pool in the constructor of InputApi
    to avoid getting tripped up by chdir manipulation.
  * Don't do the split cyclic-import check when the invoker of the
    Pylint presubmit checks explicitly sends cyclic import check
    parameters via extra_args
  * fix pseudobug where ownership of the files variable was unclear,
    and pass all arguments on stdin (instead of mix of CLI + stdin).
  * fix bug in pylint which caused it to manipulate sys.path before
    spawning its subprocesses, which caused multiprocessing to fail
    on windows.
    * Note: This may carry a slight semantic change. Before, pylint would
      add all .py files' directories to sys.path while checking any of
      them. Now in parallel mode, pylint will only add the path of the
      single file to sys.path. This behavior actually mirrors Python's
      own behavior, so the check should be more-correct than before (and
      should cut down on pylint import scanning time with very large
      sys.path's).
    * If someone encounters an issue with this, please note that the
      GetPylint check also includes an extra_paths_list which is
      expressly for this purpose.

R=dpranke@chromium.org, kbr@chromium.org, maruel@chromium.org
BUG=501012

Review URL: https://codereview.chromium.org/1208743002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@295908 0039d316-1c4b-4281-b951-d872f2087c98