Create HlsMediaSource.Manifest to hold playlist information

This allows the user to get the HlsMasterPlaylist through
Exoplayer.getCurrentManifest().

Issue:#2537

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=150232455

library/src/main/java/com/google/android/exoplayer2/source/hls/HlsManifest.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.google.android.exoplayer2.source.hls;
+
+import com.google.android.exoplayer2.source.hls.playlist.HlsMasterPlaylist;
+import com.google.android.exoplayer2.source.hls.playlist.HlsMediaPlaylist;
+
+/**
+ * Holds a master playlist along with a snapshot of one of its media playlists.
+ */
+public final class HlsManifest {
+
+  /**
+   * The master playlist of an HLS stream.
+   */
+  public final HlsMasterPlaylist masterPlaylist;
+  /**
+   * A snapshot of a media playlist referred to by {@link #masterPlaylist}.
+   */
+  public final HlsMediaPlaylist mediaPlaylist;
+
+  /**
+   * @param masterPlaylist The master playlist.
+   * @param mediaPlaylist The media playlist.
+   */
+  HlsManifest(HlsMasterPlaylist masterPlaylist, HlsMediaPlaylist mediaPlaylist) {
+    this.masterPlaylist = masterPlaylist;
+    this.mediaPlaylist = mediaPlaylist;
+  }
+
+}

library/src/main/java/com/google/android/exoplayer2/source/hls/HlsMediaSource.java

@@ -129,7 +129,8 @@ public void onPrimaryPlaylistRefreshed(HlsMediaPlaylist playlist) {
       timeline = new SinglePeriodTimeline(playlist.startTimeUs + playlist.durationUs,
           playlist.durationUs, playlist.startTimeUs, windowDefaultStartPositionUs, true, false);
     }
-    sourceListener.onSourceInfoRefreshed(timeline, playlist);
+    sourceListener.onSourceInfoRefreshed(timeline,
+        new HlsManifest(playlistTracker.getMasterPlaylist(), playlist));
   }
 
 }