Somewhere along the way, the presubmit hook for the autotest
repo sprouted a dependency on chromite.  That means the hook
will fail (at least, for certain changes) if you don't run
"utils/build_externals" prior to trying to upload.

This won't do:  We can't expect ordinary developers to diagnose
that sort of dependency, let alone actually fix it.  The only
possible response will be that developers will upload with
--no-verify, which apparently is what happens (see  bug 610777 
for a likely instance).

Below is text from a sample presbumit failure showing the
trouble:
Errors in PROJECT *chromiumos/third_party/autotest*!
    COMMIT e41a4cb0:
        Description:
            >[autotest] Change infra_FirmwareAutoupdate to reboot the DUT.
            >
            >A firmware update isn't really complete until the update target is
            >rebooted.  This makes infra_FirmwareAutoupdate a server side test, and
            >adds a call to reboot the DUT.
            >
            >BUG=chromium:214729
            >TEST=run the test in a local autotest instance
            >
            >Change-Id: I45300cb11f61702e71b33efc20f85378f1ac475d
            >
            >
        Errors:
            * Hook script "./site_utils/presubmit_hooks/check_suite_scheduler.py" failed with code 1:
              Traceback (most recent call last):
                File "./site_utils/presubmit_hooks/check_suite_scheduler.py", line 46, in <module>
                  main()
                File "./site_utils/presubmit_hooks/check_suite_scheduler.py", line 39, in main
                  output = utils.system_output(suite_scheduler + ' --sanity')
                File "/usr/local/google/home/jrbarnette/repos/cros.b/src/third_party/autotest/files/client/common_lib/base_utils.py", line 1052, in system_output
                  args=args).stdout
                File "/usr/local/google/home/jrbarnette/repos/cros.b/src/third_party/autotest/files/client/common_lib/base_utils.py", line 749, in run
                  "Command returned non-zero exit status")
              autotest_lib.client.common_lib.error.CmdError: Command </usr/local/google/home/jrbarnette/repos/cros.b/src/third_party/autotest/files/site_utils/suite_scheduler/suite_scheduler.py --sanity> failed, rc=1, Command returned non-zero exit status
              * Command: 
                  /usr/local/google/home/jrbarnette/repos/cros.b/src/third_party/autotest/f
                  iles/site_utils/suite_scheduler/suite_scheduler.py --sanity
              Exit status: 1
              Duration: 0.165740966797
              
              stderr:
              WARNING:root:Unable to import chromite.
              WARNING:root:Unable to import chromite.
              Traceback (most recent call last):
                File "/usr/local/google/home/jrbarnette/repos/cros.b/src/third_party/autotest/files/site_utils/suite_scheduler/suite_scheduler.py", line 40, in <module>
                  import board_enumerator, deduping_scheduler, driver, forgiving_config_parser
                File "/usr/local/google/home/jrbarnette/repos/cros.b/src/third_party/autotest/files/site_utils/suite_scheduler/deduping_scheduler.py", line 14, in <module>
                  from autotest_lib.server.cros.dynamic_suite import frontend_wrappers, reporting
                File "/usr/local/google/home/jrbarnette/repos/cros.b/src/third_party/autotest/files/server/cros/dynamic_suite/reporting.py", line 25, in <module>
                  from autotest_lib.site_utils  import gmail_lib
                File "/usr/local/google/home/jrbarnette/repos/cros.b/src/third_party/autotest/files/site_utils/gmail_lib.py", line 31, in <module>
                  from chromite.lib import retry_util
              ImportError: No module named chromite.lib