Allow late HLS sample queue building

Issue:#3149

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177836048

ISSUE_TEMPLATE

+*** ISSUES THAT IGNORE THIS TEMPLATE WILL BE CLOSED WITHOUT INVESTIGATION ***
+
 Before filing an issue:
 -----------------------
 - Search existing issues, including issues that are closed.

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

@@ -15,6 +15,7 @@
  */
 package com.google.android.exoplayer2.source.hls;
 
+import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.FormatHolder;
 import com.google.android.exoplayer2.decoder.DecoderInputBuffer;
 import com.google.android.exoplayer2.source.SampleStream;
@@ -25,33 +26,60 @@ import java.io.IOException;
  */
 /* package */ final class HlsSampleStream implements SampleStream {
 
-  public final int sampleQueueIndex;
-
+  private final int trackGroupIndex;
   private final HlsSampleStreamWrapper sampleStreamWrapper;
+  private int sampleQueueIndex;
 
-  public HlsSampleStream(HlsSampleStreamWrapper sampleStreamWrapper, int sampleQueueIndex) {
+  public HlsSampleStream(HlsSampleStreamWrapper sampleStreamWrapper, int trackGroupIndex) {
     this.sampleStreamWrapper = sampleStreamWrapper;
-    this.sampleQueueIndex = sampleQueueIndex;
+    this.trackGroupIndex = trackGroupIndex;
+  }
+
+  public void unbindSampleQueue() {
+    if (sampleQueueIndex != C.INDEX_UNSET) {
+      sampleStreamWrapper.unbindSampleQueue(trackGroupIndex);
+    }
   }
 
+  // SampleStream implementation.
+
   @Override
   public boolean isReady() {
-    return sampleStreamWrapper.isReady(sampleQueueIndex);
+    return ensureBoundSampleQueue() && sampleStreamWrapper.isReady(sampleQueueIndex);
   }
 
   @Override
   public void maybeThrowError() throws IOException {
+    if (!ensureBoundSampleQueue()) {
+      throw new SampleQueueMappingException(
+          sampleStreamWrapper.getTrackGroups().get(trackGroupIndex).getFormat(0).sampleMimeType);
+    }
     sampleStreamWrapper.maybeThrowError();
   }
 
   @Override
   public int readData(FormatHolder formatHolder, DecoderInputBuffer buffer, boolean requireFormat) {
+    if (!ensureBoundSampleQueue()) {
+      return C.RESULT_NOTHING_READ;
+    }
     return sampleStreamWrapper.readData(sampleQueueIndex, formatHolder, buffer, requireFormat);
   }
 
   @Override
   public int skipData(long positionUs) {
+    if (!ensureBoundSampleQueue()) {
+      return 0;
+    }
     return sampleStreamWrapper.skipData(sampleQueueIndex, positionUs);
   }
 
+  // Internal methods.
+
+  private boolean ensureBoundSampleQueue() {
+    if (sampleQueueIndex != C.INDEX_UNSET) {
+      return true;
+    }
+    sampleQueueIndex = sampleStreamWrapper.bindSampleQueueToSampleStream(trackGroupIndex);
+    return sampleQueueIndex != C.INDEX_UNSET;
+  }
 }

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

+/*
+ * 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.SampleQueue;
+import com.google.android.exoplayer2.source.TrackGroup;
+import java.io.IOException;
+
+/** Thrown when it is not possible to map a {@link TrackGroup} to a {@link SampleQueue}. */
+public final class SampleQueueMappingException extends IOException {
+
+  /** @param mimeType The mime type of the track group whose mapping failed. */
+  public SampleQueueMappingException(String mimeType) {
+    super("Unable to bind a sample queue to TrackGroup with mime type " + mimeType + ".");
+  }
+}