Enable ui_struct_traits_unittests on try bots.

testing/buildbot/chromium.linux.json

 {
   "Android Arm64 Builder (dbg)": {
     "additional_compile_targets": [
       "all"
     ]
   },
   "Android Builder": {
     "additional_compile_targets": [
       "cronet_test_instrumentation_apk",
       "system_webview_apk"
@@ skipping 1392 matching lines @@
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "ui_base_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
+        "test": "ui_struct_traits_unittests"
+      },
+      {
+        "swarming": {
+          "can_use_on_swarming_builders": true
+        },
         "test": "ui_touch_selection_unittests"
       },
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "unit_tests"
       },
       {
         "swarming": {
@@ skipping 831 matching lines @@
         "override_compile_targets": [
           "telemetry_unittests_run"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       }
     ]
   }
 }