BuildTargetUnitTest: Add empty sysroot option.

BUG=None
TEST=run_tests

Cq-Depend: chromium:1606067
Change-Id: I2ff9d3bbc8b4f00fc869cfaebc0a58b63471e449
Reviewed-on: https://chromium-review.googlesource.com/1605368
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
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/test.py b/api/controller/test.py
index 428a8b1..aa0d541 100644
--- a/api/controller/test.py
+++ b/api/controller/test.py
@@ -55,6 +55,10 @@
   if not result_path:
     cros_build_lib.Die('result_path is required.')
 
+  # Method flags.
+  # An empty sysroot means build packages was not run.
+  was_built = not input_proto.flags.empty_sysroot
+
   # Chroot handling.
   chroot = input_proto.chroot.path
   cache_dir = input_proto.chroot.cache_dir
@@ -80,7 +84,7 @@
 
     try:
       commands.RunUnitTests(constants.SOURCE_ROOT, board, extra_env=extra_env,
-                            chroot_args=chroot_args)
+                            chroot_args=chroot_args, build_stage=was_built)
     except failures_lib.PackageBuildFailure as e:
       # Add the failed packages.
       for pkg in e.failed_packages: