Add closure_compilation to `git cl try` for CLs that touch resources

ui/webui/resources/PRESUBMIT.py

Index: ui/webui/resources/PRESUBMIT.py
diff --git a/ui/webui/resources/PRESUBMIT.py b/ui/webui/resources/PRESUBMIT.py
index 2ac87faf2b09787c19200dad102e395811d7661e..71e127247225f528a243c37b3493b96a75610a68 100644
--- a/ui/webui/resources/PRESUBMIT.py
+++ b/ui/webui/resources/PRESUBMIT.py
@@ -26,3 +26,11 @@ def PostUploadHook(cl, change, output_api):
   rietveld_obj.update_description(cl.issue, new_description)
   return [output_api.PresubmitNotifyResult(
       'Automatically added optional Closure bots to run on CQ.')]
+
+
+def GetPreferredTryMasters(project, change):
+  return {
+    'tryserver.chromium.linux': {
+      'closure_compilation': set(['defaulttests']),
+    },
+  }