Build API: Add ImageService/CreateVm method.

BUG=chromium:957758, b:131710961
TEST=run_tests
Cq-Depend: chromium:1592723, chromium:1593932

Change-Id: Id2a481d3e22243ba2846279f61d55713b40983d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1593420
Commit-Queue: Alex Klein <saklein@chromium.org>
Tested-by: Alex Klein <saklein@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Evan Hernandez <evanhernandez@chromium.org>
diff --git a/api/controller/controller_util.py b/api/controller/controller_util.py
index f2d879a..b12f952 100644
--- a/api/controller/controller_util.py
+++ b/api/controller/controller_util.py
@@ -7,9 +7,18 @@
 
 from __future__ import print_function
 
+from chromite.lib import chroot_lib
 from chromite.lib import portage_util
 
 
+def ParseChroot(chroot_message):
+  """Create a chroot object from the chroot message."""
+  path = chroot_message.path
+  cache_dir = chroot_message.cache_dir
+
+  return chroot_lib.Chroot(path=path, cache_dir=cache_dir)
+
+
 def CPVToPackageInfo(cpv, package_info):
   """Helper to translate CPVs into a PackageInfo message."""
   package_info.package_name = cpv.package