[SPARK-7347] DAG visualization: add tooltips to RDDs

This is an addition to #5729.

Here's an example with ALS.
<img src="https://issues.apache.org/jira/secure/attachment/12731039/tooltip.png" width="400px"></img>

Author: Andrew Or <andrew@databricks.com>

Closes #5957 from andrewor14/viz-hover2 and squashes the following commits:

60e3758 [Andrew Or] Add tooltips for RDDs on job page

1 files changed, 3 insertions, 2 deletions

diff --git a/core/src/main/scala/org/apache/spark/ui/scope/RDDOperationGraph.scala b/core/src/main/scala/org/apache/spark/ui/scope/RDDOperationGraph.scala
index edf005f7f3..2b2db9e62b 100644
--- a/core/src/main/scala/org/apache/spark/ui/scope/RDDOperationGraph.scala
+++ b/core/src/main/scala/org/apache/spark/ui/scope/RDDOperationGraph.scala
@@ -178,10 +178,11 @@ private[ui] object RDDOperationGraph extends Logging {
    * On the stage page, it is displayed as a box with an embedded label.
    */
   private def makeDotNode(node: RDDOperationNode, forJob: Boolean): String = {
+    val label = s"${node.name} (${node.id})"
     if (forJob) {
-      s"""${node.id} [label=" " shape="circle" padding="5" labelStyle="font-size: 0"]"""
+      s"""${node.id} [label="$label" shape="circle" padding="5" labelStyle="font-size: 0"]"""
     } else {
-      s"""${node.id} [label="${node.name} (${node.id})" padding="5" labelStyle="font-size: 10"]"""
+      s"""${node.id} [label="$label" padding="5" labelStyle="font-size: 10"]"""
     }
   }