Add MediaChunkIterator interface and DASH implementation.

This will allow to provide available information about future chunks to the
track selection.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=202940994

library/core/src/main/java/com/google/android/exoplayer2/source/chunk/MediaChunkIterator.java

@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) 2018 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.chunk;
+
+import com.google.android.exoplayer2.upstream.DataSpec;
+import java.util.NoSuchElementException;
+
+/**
+ * Iterator for media chunk sequences.
+ *
+ * <p>The iterator initially points in front of the first available element. The first call to
+ * {@link #next()} moves the iterator to the first element. Check the return value of {@link
+ * #next()} or {@link #isEnded()} to determine whether the iterator reached the end of the available
+ * data.
+ */
+public interface MediaChunkIterator {
+
+  /** An empty media chunk iterator without available data. */
+  MediaChunkIterator EMPTY =
+      new MediaChunkIterator() {
+        @Override
+        public boolean isEnded() {
+          return true;
+        }
+
+        @Override
+        public boolean next() {
+          return false;
+        }
+
+        @Override
+        public DataSpec getDataSpec() {
+          throw new NoSuchElementException();
+        }
+
+        @Override
+        public long getChunkStartTimeUs() {
+          throw new NoSuchElementException();
+        }
+
+        @Override
+        public long getChunkEndTimeUs() {
+          throw new NoSuchElementException();
+        }
+      };
+
+  /** Returns whether the iteration has reached the end of the available data. */
+  boolean isEnded();
+
+  /**
+   * Moves the iterator to the next media chunk.
+   *
+   * <p>Check the return value or {@link #isEnded()} to determine whether the iterator reached the
+   * end of the available data.
+   *
+   * @return Whether the iterator points to a media chunk with available data.
+   */
+  boolean next();
+
+  /**
+   * Returns the {@link DataSpec} used to load the media chunk.
+   *
+   * @throws java.util.NoSuchElementException If the method is called before the first call to
+   *     {@link #next()} or when {@link #isEnded()} is true.
+   */
+  DataSpec getDataSpec();
+
+  /**
+   * Returns the media start time of the chunk, in microseconds.
+   *
+   * @throws java.util.NoSuchElementException If the method is called before the first call to
+   *     {@link #next()} or when {@link #isEnded()} is true.
+   */
+  long getChunkStartTimeUs();
+
+  /**
+   * Returns the media end time of the chunk, in microseconds.
+   *
+   * @throws java.util.NoSuchElementException If the method is called before the first call to
+   *     {@link #next()} or when {@link #isEnded()} is true.
+   */
+  long getChunkEndTimeUs();
+}

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

@@ -37,6 +37,7 @@ import com.google.android.exoplayer2.source.chunk.ChunkedTrackBlacklistUtil;
 import com.google.android.exoplayer2.source.chunk.ContainerMediaChunk;
 import com.google.android.exoplayer2.source.chunk.InitializationChunk;
 import com.google.android.exoplayer2.source.chunk.MediaChunk;
+import com.google.android.exoplayer2.source.chunk.MediaChunkIterator;
 import com.google.android.exoplayer2.source.chunk.SingleSampleMediaChunk;
 import com.google.android.exoplayer2.source.dash.PlayerEmsgHandler.PlayerTrackEmsgHandler;
 import com.google.android.exoplayer2.source.dash.manifest.AdaptationSet;
@@ -54,6 +55,7 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.NoSuchElementException;
 
 /**
  * A default {@link DashChunkSource} implementation.
@@ -503,6 +505,70 @@ public class DefaultDashChunkSource implements DashChunkSource {
 
   // Protected classes.
 
+  /** {@link MediaChunkIterator} wrapping a {@link RepresentationHolder}. */
+  protected static final class RepresentationSegmentIterator implements MediaChunkIterator {
+
+    private final RepresentationHolder representationHolder;
+    private final long firstSegmentNum;
+    private final long lastAvailableSegmentNum;
+
+    private long segmentNum;
+
+    /**
+     * Creates iterator.
+     *
+     * @param representation The {@link RepresentationHolder} to wrap.
+     * @param segmentNum The number of the segment this iterator will be pointing to initially.
+     * @param lastAvailableSegmentNum The number of the last available segment.
+     */
+    public RepresentationSegmentIterator(
+        RepresentationHolder representation, long segmentNum, long lastAvailableSegmentNum) {
+      this.representationHolder = representation;
+      this.firstSegmentNum = segmentNum;
+      this.segmentNum = segmentNum - 1;
+      this.lastAvailableSegmentNum = lastAvailableSegmentNum;
+    }
+
+    @Override
+    public boolean isEnded() {
+      return segmentNum > lastAvailableSegmentNum;
+    }
+
+    @Override
+    public boolean next() {
+      segmentNum++;
+      return segmentNum <= lastAvailableSegmentNum;
+    }
+
+    @Override
+    public @Nullable DataSpec getDataSpec() {
+      checkInBounds();
+      Representation representation = representationHolder.representation;
+      RangedUri segmentUri = representationHolder.getSegmentUrl(segmentNum);
+      Uri resolvedUri = segmentUri.resolveUri(representation.baseUrl);
+      String cacheKey = representation.getCacheKey();
+      return new DataSpec(resolvedUri, segmentUri.start, segmentUri.length, cacheKey);
+    }
+
+    @Override
+    public long getChunkStartTimeUs() {
+      checkInBounds();
+      return representationHolder.getSegmentStartTimeUs(segmentNum);
+    }
+
+    @Override
+    public long getChunkEndTimeUs() {
+      checkInBounds();
+      return representationHolder.getSegmentEndTimeUs(segmentNum);
+    }
+
+    private void checkInBounds() {
+      if (segmentNum < firstSegmentNum || segmentNum > lastAvailableSegmentNum) {
+        throw new NoSuchElementException();
+      }
+    }
+  }
+
   /** Holds information about a snapshot of a single {@link Representation}. */
   protected static final class RepresentationHolder {