Add DashDownloader helper class to download dash streams

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=151456161

library/core/src/main/java/com/google/android/exoplayer2/C.java

@@ -541,10 +541,19 @@ public final class C {
 
   /**
    * Priority for media playback.
+   *
+   * <p>Larger values indicate higher priorities.
    */
   public static final int PRIORITY_PLAYBACK = 0;
 
   /**
+   * Priority for media downloading.
+   *
+   * <p>Larger values indicate higher priorities.
+   */
+  public static final int PRIORITY_DOWNLOAD = PRIORITY_PLAYBACK - 1000;
+
+  /**
    * Converts a time in microseconds to the corresponding time in milliseconds, preserving
    * {@link #TIME_UNSET} values.
    *

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/CacheDataSource.java

@@ -109,6 +109,15 @@ public final class CacheDataSource implements DataSource {
   private long totalCachedBytesRead;
 
   /**
+   * Generates a cache key out of the given {@link Uri}.
+   *
+   * @param uri Uri of a content which the requested key is for.
+   */
+  public static String generateKey(Uri uri) {
+    return uri.toString();
+  }
+
+  /**
    * Constructs an instance with default {@link DataSource} and {@link DataSink} instances for
    * reading and writing the cache and with {@link #DEFAULT_MAX_CACHE_FILE_SIZE}.
    */
@@ -171,7 +180,7 @@ public final class CacheDataSource implements DataSource {
     try {
       uri = dataSpec.uri;
       flags = dataSpec.flags;
-      key = dataSpec.key != null ? dataSpec.key : uri.toString();
+      key = dataSpec.key != null ? dataSpec.key : generateKey(dataSpec.uri);
       readPosition = dataSpec.position;
       currentRequestIgnoresCache = (ignoreCacheOnError && seenCacheError)
           || (dataSpec.length == C.LENGTH_UNSET && ignoreCacheForUnsetLengthRequests);

library/core/src/main/java/com/google/android/exoplayer2/util/PriorityTaskManager.java

@@ -54,7 +54,7 @@ public final class PriorityTaskManager {
   /**
    * Register a new task. The task must call {@link #remove(int)} when done.
    *
-   * @param priority The priority of the task.
+   * @param priority The priority of the task. Larger values indicate higher priorities.
    */
   public void add(int priority) {
     synchronized (lock) {

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

@@ -48,14 +48,14 @@ public final class DashUtil {
    * Loads a DASH manifest.
    *
    * @param dataSource The {@link HttpDataSource} from which the manifest should be read.
-   * @param manifestUriString The URI of the manifest to be read.
+   * @param manifestUri The URI of the manifest to be read.
    * @return An instance of {@link DashManifest}.
    * @throws IOException Thrown when there is an error while loading.
    */
-  public static DashManifest loadManifest(DataSource dataSource, String manifestUriString)
+  public static DashManifest loadManifest(DataSource dataSource, String manifestUri)
       throws IOException {
     DataSourceInputStream inputStream = new DataSourceInputStream(dataSource,
-        new DataSpec(Uri.parse(manifestUriString), DataSpec.FLAG_ALLOW_CACHING_UNKNOWN_LENGTH));
+        new DataSpec(Uri.parse(manifestUri), DataSpec.FLAG_ALLOW_CACHING_UNKNOWN_LENGTH));
     try {
       inputStream.open();
       DashManifestParser parser = new DashManifestParser();

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

@@ -22,7 +22,7 @@ import com.google.android.exoplayer2.source.dash.manifest.RangedUri;
  * An implementation of {@link DashSegmentIndex} that wraps a {@link ChunkIndex} parsed from a
  * media stream.
  */
-/* package */ final class DashWrappingSegmentIndex implements DashSegmentIndex {
+public final class DashWrappingSegmentIndex implements DashSegmentIndex {
 
   private final ChunkIndex chunkIndex;
 

playbacktests/src/androidTest/java/com/google/android/exoplayer2/playbacktests/gts/DashTest.java → playbacktests/src/androidTest/java/com/google/android/exoplayer2/playbacktests/gts/DashStreamingTest.java

@@ -28,9 +28,9 @@ import com.google.android.exoplayer2.util.Util;
 /**
  * Tests DASH playbacks using {@link ExoPlayer}.
  */
-public final class DashTest extends ActivityInstrumentationTestCase2<HostActivity> {
+public final class DashStreamingTest extends ActivityInstrumentationTestCase2<HostActivity> {
 
-  private static final String TAG = "DashTest";
+  private static final String TAG = "DashStreamingTest";
 
   private static final ActionSchedule SEEKING_SCHEDULE = new ActionSchedule.Builder(TAG)
       .delay(10000).seek(15000)
@@ -72,7 +72,7 @@ public final class DashTest extends ActivityInstrumentationTestCase2<HostActivit
   
   private DashTestRunner testRunner;
 
-  public DashTest() {
+  public DashStreamingTest() {
     super(HostActivity.class);
   }
 

playbacktests/src/androidTest/java/com/google/android/exoplayer2/playbacktests/gts/DashTestData.java

@@ -18,7 +18,7 @@ package com.google.android.exoplayer2.playbacktests.gts;
 import com.google.android.exoplayer2.util.Util;
 
 /**
- * Test data for {@link DashTest} and {@link DashWidevineOfflineTest).
+ * Test data for DASH tests.
  */
 public final class DashTestData {