Adds support for the messageData attribute of the Event element in DASH MPDs for ExoPlayer.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=211854408

RELEASENOTES.md

@@ -38,6 +38,8 @@
     ([#4422](https://github.com/google/ExoPlayer/issues/4422)).
     ([#4422](https://github.com/google/ExoPlayer/issues/4422)).
   * Fix the bitrate being unset on primary track sample formats
   * Fix the bitrate being unset on primary track sample formats
     ([#3297](https://github.com/google/ExoPlayer/issues/3297)).
     ([#3297](https://github.com/google/ExoPlayer/issues/3297)).
+* DASH:
+  * Support messageData attribute of in-manifest events.
 * Improve seeking support for progressive streams:
 * Improve seeking support for progressive streams:
   * Support seeking in MPEG-TS
   * Support seeking in MPEG-TS
     ([#966](https://github.com/google/ExoPlayer/issues/966)).
     ([#966](https://github.com/google/ExoPlayer/issues/966)).

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/manifest/DashManifestParser.java

@@ -838,8 +838,15 @@ public class DashManifestParser extends DefaultHandler
     long durationMs = Util.scaleLargeTimestamp(duration, 1000, timescale);
     long durationMs = Util.scaleLargeTimestamp(duration, 1000, timescale);
     long presentationTimesUs = Util.scaleLargeTimestamp(presentationTime, C.MICROS_PER_SECOND,
     long presentationTimesUs = Util.scaleLargeTimestamp(presentationTime, C.MICROS_PER_SECOND,
         timescale);
         timescale);
+    String messageData = parseString(xpp, "messageData", null);
     byte[] eventObject = parseEventObject(xpp, scratchOutputStream);
     byte[] eventObject = parseEventObject(xpp, scratchOutputStream);
-    return buildEvent(schemeIdUri, value, id, durationMs, eventObject, presentationTimesUs);
+    return buildEvent(
+        schemeIdUri,
+        value,
+        id,
+        durationMs,
+        messageData == null ? eventObject : Util.getUtf8Bytes(messageData),
+        presentationTimesUs);
   }
   }
 
 
   /**
   /**

library/dash/src/test/assets/sample_mpd_4_event_stream

@@ -2,7 +2,7 @@
 <MPD xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="urn:mpeg:DASH:schema:MPD:2011" xmlns:yt="http://youtube.com/yt/2012/10/10" xsi:schemaLocation="urn:mpeg:DASH:schema:MPD:2011 DASH-MPD.xsd" minBufferTime="PT1.500S" profiles="urn:mpeg:dash:profile:isoff-main:2011" type="dynamic" availabilityStartTime="2016-10-14T17:00:17" timeShiftBufferDepth="PT7200.000S" minimumUpdatePeriod="PT2.000S" yt:earliestMediaSequence="0" yt:mpdRequestTime="2016-10-14T18:29:17.082" yt:mpdResponseTime="2016-10-14T18:29:17.194">
 <MPD xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="urn:mpeg:DASH:schema:MPD:2011" xmlns:yt="http://youtube.com/yt/2012/10/10" xsi:schemaLocation="urn:mpeg:DASH:schema:MPD:2011 DASH-MPD.xsd" minBufferTime="PT1.500S" profiles="urn:mpeg:dash:profile:isoff-main:2011" type="dynamic" availabilityStartTime="2016-10-14T17:00:17" timeShiftBufferDepth="PT7200.000S" minimumUpdatePeriod="PT2.000S" yt:earliestMediaSequence="0" yt:mpdRequestTime="2016-10-14T18:29:17.082" yt:mpdResponseTime="2016-10-14T18:29:17.194">
  <Period start="PT0.000S" yt:segmentIngestTime="2016-10-14T17:00:14.257">
  <Period start="PT0.000S" yt:segmentIngestTime="2016-10-14T17:00:14.257">
    <EventStream schemeIdUri="urn:uuid:XYZY" timescale="1000" value="call">
    <EventStream schemeIdUri="urn:uuid:XYZY" timescale="1000" value="call">
-     <Event presentationTime="0" duration="10000" id="0">+ 1 800 10101010</Event>
+     <Event presentationTime="0" duration="10000" id="0" messageData="+ 1 800 10101010"/>
    </EventStream>
    </EventStream>
    <EventStream schemeIdUri="urn:dvb:iptv:cpm:2014">
    <EventStream schemeIdUri="urn:dvb:iptv:cpm:2014">
      <Event presentationTime="300" duration="1500" id="1"><![CDATA[<BroadcastEvent>
      <Event presentationTime="300" duration="1500" id="1"><![CDATA[<BroadcastEvent>