Add freon support in run_chrome_test_binary()

There's no X environment to worry about, so just run the test. This
works for security_SandboxLinuxUnittests, at least.

BUG=chromium:428080
TEST=ran security_SandboxLinuxUnittests on link_freon

Change-Id: I6a84bd28c15cf0d9a32ed4d9c36cfe682ac9d165
Reviewed-on: https://chromium-review.googlesource.com/225569
Reviewed-by: Ilja Friedel <ihf@chromium.org>
Tested-by: Michael Spang <spang@chromium.org>
Commit-Queue: Michael Spang <spang@chromium.org>
diff --git a/client/cros/chrome_binary_test.py b/client/cros/chrome_binary_test.py
index c358af0..ac81238 100755
--- a/client/cros/chrome_binary_test.py
+++ b/client/cros/chrome_binary_test.py
@@ -63,10 +63,16 @@
         cmd = '%s %s' % (env_vars, prefix + cmd)
 
         try:
-            if as_chronos:
-                graphics_utils.xsystem(cmd, user='chronos')
+            if utils.is_freon():
+                if as_chronos:
+                    utils.system('su %s -c \'%s\'' % ('chronos', cmd))
+                else:
+                    utils.system(cmd)
             else:
-                graphics_utils.xsystem(cmd)
+                if as_chronos:
+                    graphics_utils.xsystem(cmd, user='chronos')
+                else:
+                    graphics_utils.xsystem(cmd)
         except error.CmdError as e:
             raise error.TestFail('%s failed! %s' % (binary_to_run, e))