[SPARK-17623][CORE] Clarify type of TaskEndReason with a failed task.

## What changes were proposed in this pull request?

In TaskResultGetter, enqueueFailedTask currently deserializes the result
as a TaskEndReason. But the type is actually more specific, its a
TaskFailedReason. This just leads to more blind casting later on – it
would be more clear if the msg was cast to the right type immediately,
so method parameter types could be tightened.

## How was this patch tested?

Existing unit tests via jenkins.  Note that the code was already performing a blind-cast to a TaskFailedReason before in any case, just in a different spot, so there shouldn't be any behavior change.

Author: Imran Rashid <irashid@cloudera.com>

Closes #15181 from squito/SPARK-17623.

1 files changed, 1 insertions, 1 deletions

diff --git a/core/src/test/scala/org/apache/spark/util/JsonProtocolSuite.scala b/core/src/test/scala/org/apache/spark/util/JsonProtocolSuite.scala
index c89be22a34..00314abf49 100644
--- a/core/src/test/scala/org/apache/spark/util/JsonProtocolSuite.scala
+++ b/core/src/test/scala/org/apache/spark/util/JsonProtocolSuite.scala
@@ -146,7 +146,7 @@ class JsonProtocolSuite extends SparkFunSuite {
     val fetchFailed = FetchFailed(BlockManagerId("With or", "without you", 15), 17, 18, 19,
       "Some exception")
     val fetchMetadataFailed = new MetadataFetchFailedException(17,
-      19, "metadata Fetch failed exception").toTaskEndReason
+      19, "metadata Fetch failed exception").toTaskFailedReason
     val exceptionFailure = new ExceptionFailure(exception, Seq.empty[AccumulableInfo])
     testTaskEndReason(Success)
     testTaskEndReason(Resubmitted)