platform/dev: add chromite import for internal use in package.

If dev is called as a package, __init__.py can offer a chromite dependency for
it. But __init__.py cannot handle the internal calls.

dev/
    __init__.py
    A.py
    B.py

C.py import package dev, and call functions in A.py, it will succeed.

But if B.py directly calls 'python A.py', or import A to call its funcions, it
will fail.

This CL handles this case.

BUG=chromium:636467
TEST=locally run python cros_update.py, cros_update_progress.py. Run cros
flash.

Change-Id: I69d931b3a20a72a9e33f121f64382004f527cd42
Reviewed-on: https://chromium-review.googlesource.com/375040
Commit-Ready: Xixuan Wu <xixuan@chromium.org>
Tested-by: Xixuan Wu <xixuan@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/cros_update.py b/cros_update.py
index 78187c1..6bf3e3f 100644
--- a/cros_update.py
+++ b/cros_update.py
@@ -30,6 +30,8 @@
 import os
 import sys
 
+# only import setup_chromite before chromite import.
+import setup_chromite # pylint: disable=unused-import
 try:
   from chromite.lib import auto_updater
   from chromite.lib import remote_access
@@ -38,6 +40,7 @@
   logging.debug('chromite cannot be imported: %r', e)
   auto_updater = None
   remote_access = None
+  timeout_util = None
 
 # Timeout for CrOS auto-update process.
 CROS_UPDATE_TIMEOUT_MIN = 30