Make GomaConfig.DEFAULT map to a Goma RBE cros build.

Now, let me make ChromeOS builders use ?cros Goma RBE instance by default.

BUG=b:162292728
TEST=./run_pytest

Change-Id: If3f20c9a69c4bbcc3b26ffc2b474f456e51e8e4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2616045
Reviewed-by: LaMont Jones <lamontjones@chromium.org>
Reviewed-by: Sean McAllister <smcallis@google.com>
Tested-by: LaMont Jones <lamontjones@chromium.org>
Commit-Queue: LaMont Jones <lamontjones@chromium.org>
Commit-Queue: Sean McAllister <smcallis@google.com>
Auto-Submit: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
diff --git a/api/controller/controller_util.py b/api/controller/controller_util.py
index df045bc..ec46ebf 100644
--- a/api/controller/controller_util.py
+++ b/api/controller/controller_util.py
@@ -73,10 +73,10 @@
   if goma_message.goma_approach == common_pb2.GomaConfig.RBE_STAGING:
     goma_approach = goma_util.GomaApproach('?staging',
                                            'staging-goma.chromium.org', True)
-  elif goma_message.goma_approach == common_pb2.GomaConfig.RBE_CHROMEOS:
-    goma_approach = goma_util.GomaApproach('?cros', 'goma.chromium.org', True)
-  else:
+  elif goma_message.goma_approach == common_pb2.GomaConfig.RBE_PROD:
     goma_approach = goma_util.GomaApproach('?prod', 'goma.chromium.org', True)
+  else:
+    goma_approach = goma_util.GomaApproach('?cros', 'goma.chromium.org', True)
 
   # Note that we are not specifying the goma log_dir so that goma will create
   # and use a tmp dir for the logs.