Make TaskDetailsClassNames private[spark]

Author: kayousterhout

core/src/main/scala/org/apache/spark/ui/jobs/TaskDetailsClassNames.scala

@@ -24,7 +24,7 @@ package org.apache.spark.ui.jobs
  * If new optional metrics are added here, they should also be added to the end of webui.css
  * to have the style set to "display: none;" by default.
  */
-private object TaskDetailsClassNames {
+private[spark] object TaskDetailsClassNames {
   val SCHEDULER_DELAY = "scheduler_delay"
   val TASK_DESERIALIZATION_TIME = "deserialization_time"
   val RESULT_SERIALIZATION_TIME = "serialization_time"