Chroot: Add chrome root support.

Added chrome root support to the chroot_lib, controller_util,
and field_handler tests.
Added --chrome-root version of the argument so it has the more
modern version of the argument available.

BUG=chromium:980611
TEST=run_tests

Change-Id: I8d3c6641f17ea92b38e0d866b564ac5a9d946e10
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1684465
Tested-by: Alex Klein <saklein@chromium.org>
Reviewed-by: Sean Abraham <seanabraham@chromium.org>
Commit-Queue: Alex Klein <saklein@chromium.org>
diff --git a/api/controller/controller_util.py b/api/controller/controller_util.py
index 17156ee..21f6d84 100644
--- a/api/controller/controller_util.py
+++ b/api/controller/controller_util.py
@@ -15,6 +15,7 @@
   """Create a chroot object from the chroot message."""
   path = chroot_message.path
   cache_dir = chroot_message.cache_dir
+  chrome_root = chroot_message.chrome_dir
 
   use_flags = [u.flag for u in chroot_message.env.use_flags]
   features = [f.feature for f in chroot_message.env.features]
@@ -28,7 +29,8 @@
   if features:
     env['FEATURES'] = ' '.join(features)
 
-  return chroot_lib.Chroot(path=path, cache_dir=cache_dir, env=env)
+  return chroot_lib.Chroot(path=path, cache_dir=cache_dir,
+                           chrome_root=chrome_root, env=env)
 
 
 def CPVToPackageInfo(cpv, package_info):