Add forwarding timeline to prevent repetition of boiler-plate code.

Multiple timelines work as a wrapper around another timeline and forward
most of the method calls to the wrapped timeline. Added a base class meant to
be overridden which handles all the boiler-plate forwarding.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=164117264

extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/SinglePeriodAdTimeline.java

@@ -17,14 +17,14 @@ package com.google.android.exoplayer2.ext.ima;
 
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Timeline;
+import com.google.android.exoplayer2.source.ForwardingTimeline;
 import com.google.android.exoplayer2.util.Assertions;
 
 /**
  * A {@link Timeline} for sources that have ads.
  */
-public final class SinglePeriodAdTimeline extends Timeline {
+public final class SinglePeriodAdTimeline extends ForwardingTimeline {
 
-  private final Timeline contentTimeline;
   private final long[] adGroupTimesUs;
   private final int[] adCounts;
   private final int[] adsLoadedCounts;
@@ -52,9 +52,9 @@ public final class SinglePeriodAdTimeline extends Timeline {
   public SinglePeriodAdTimeline(Timeline contentTimeline, long[] adGroupTimesUs, int[] adCounts,
       int[] adsLoadedCounts, int[] adsPlayedCounts, long[][] adDurationsUs,
       long adResumePositionUs) {
+    super(contentTimeline);
     Assertions.checkState(contentTimeline.getPeriodCount() == 1);
     Assertions.checkState(contentTimeline.getWindowCount() == 1);
-    this.contentTimeline = contentTimeline;
     this.adGroupTimesUs = adGroupTimesUs;
     this.adCounts = adCounts;
     this.adsLoadedCounts = adsLoadedCounts;
@@ -63,34 +63,13 @@ public final class SinglePeriodAdTimeline extends Timeline {
     this.adResumePositionUs = adResumePositionUs;
   }
 
-  @Override
-  public int getWindowCount() {
-    return 1;
-  }
-
-  @Override
-  public Window getWindow(int windowIndex, Window window, boolean setIds,
-      long defaultPositionProjectionUs) {
-    return contentTimeline.getWindow(windowIndex, window, setIds, defaultPositionProjectionUs);
-  }
-
-  @Override
-  public int getPeriodCount() {
-    return 1;
-  }
-
   @Override
   public Period getPeriod(int periodIndex, Period period, boolean setIds) {
-    contentTimeline.getPeriod(periodIndex, period, setIds);
+    timeline.getPeriod(periodIndex, period, setIds);
     period.set(period.id, period.uid, period.windowIndex, period.durationUs,
         period.getPositionInWindowUs(), adGroupTimesUs, adCounts, adsLoadedCounts, adsPlayedCounts,
         adDurationsUs, adResumePositionUs);
     return period;
   }
 
-  @Override
-  public int getIndexOfPeriod(Object uid) {
-    return contentTimeline.getIndexOfPeriod(uid);
-  }
-
 }

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

@@ -17,7 +17,6 @@ package com.google.android.exoplayer2.source;
 
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.ExoPlayer;
-import com.google.android.exoplayer2.Player.RepeatMode;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.upstream.Allocator;
 import com.google.android.exoplayer2.util.Assertions;
@@ -128,9 +127,8 @@ public final class ClippingMediaSource implements MediaSource, MediaSource.Liste
   /**
    * Provides a clipped view of a specified timeline.
    */
-  private static final class ClippingTimeline extends Timeline {
+  private static final class ClippingTimeline extends ForwardingTimeline {
 
-    private final Timeline timeline;
     private final long startUs;
     private final long endUs;
 
@@ -143,6 +141,7 @@ public final class ClippingMediaSource implements MediaSource, MediaSource.Liste
      *     of {@code timeline}, or {@link C#TIME_END_OF_SOURCE} to clip no samples from the end.
      */
     public ClippingTimeline(Timeline timeline, long startUs, long endUs) {
+      super(timeline);
       Assertions.checkArgument(timeline.getWindowCount() == 1);
       Assertions.checkArgument(timeline.getPeriodCount() == 1);
       Window window = timeline.getWindow(0, new Window(), false);
@@ -155,26 +154,10 @@ public final class ClippingMediaSource implements MediaSource, MediaSource.Liste
       }
       Period period = timeline.getPeriod(0, new Period());
       Assertions.checkArgument(period.getPositionInWindowUs() == 0);
-      this.timeline = timeline;
       this.startUs = startUs;
       this.endUs = resolvedEndUs;
     }
 
-    @Override
-    public int getWindowCount() {
-      return 1;
-    }
-
-    @Override
-    public int getNextWindowIndex(int windowIndex, @RepeatMode int repeatMode) {
-      return timeline.getNextWindowIndex(windowIndex, repeatMode);
-    }
-
-    @Override
-    public int getPreviousWindowIndex(int windowIndex, @RepeatMode int repeatMode) {
-      return timeline.getPreviousWindowIndex(windowIndex, repeatMode);
-    }
-
     @Override
     public Window getWindow(int windowIndex, Window window, boolean setIds,
         long defaultPositionProjectionUs) {
@@ -196,11 +179,6 @@ public final class ClippingMediaSource implements MediaSource, MediaSource.Liste
       return window;
     }
 
-    @Override
-    public int getPeriodCount() {
-      return 1;
-    }
-
     @Override
     public Period getPeriod(int periodIndex, Period period, boolean setIds) {
       period = timeline.getPeriod(0, period, setIds);
@@ -208,11 +186,6 @@ public final class ClippingMediaSource implements MediaSource, MediaSource.Liste
       return period;
     }
 
-    @Override
-    public int getIndexOfPeriod(Object uid) {
-      return timeline.getIndexOfPeriod(uid);
-    }
-
   }
 
 }

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

@@ -0,0 +1,68 @@
+/*
+ * 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;
+
+import com.google.android.exoplayer2.Player;
+import com.google.android.exoplayer2.Timeline;
+
+/**
+ * An overridable {@link Timeline} implementation forwarding all methods to another timeline.
+ */
+public abstract class ForwardingTimeline extends Timeline {
+
+  protected final Timeline timeline;
+
+  public ForwardingTimeline(Timeline timeline) {
+    this.timeline = timeline;
+  }
+
+  @Override
+  public int getWindowCount() {
+    return timeline.getWindowCount();
+  }
+
+  @Override
+  public int getNextWindowIndex(int windowIndex, @Player.RepeatMode int repeatMode) {
+    return timeline.getNextWindowIndex(windowIndex, repeatMode);
+  }
+
+  @Override
+  public int getPreviousWindowIndex(int windowIndex, @Player.RepeatMode int repeatMode) {
+    return timeline.getPreviousWindowIndex(windowIndex, repeatMode);
+  }
+
+  @Override
+  public Window getWindow(int windowIndex, Window window, boolean setIds,
+      long defaultPositionProjectionUs) {
+    return timeline.getWindow(windowIndex, window, setIds, defaultPositionProjectionUs);
+  }
+
+  @Override
+  public int getPeriodCount() {
+    return timeline.getPeriodCount();
+  }
+
+  @Override
+  public Period getPeriod(int periodIndex, Period period, boolean setIds) {
+    return timeline.getPeriod(periodIndex, period, setIds);
+  }
+
+  @Override
+  public int getIndexOfPeriod(Object uid) {
+    return timeline.getIndexOfPeriod(uid);
+  }
+
+}

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

@@ -160,53 +160,25 @@ public final class LoopingMediaSource implements MediaSource {
 
   }
 
-  private static final class InfinitelyLoopingTimeline extends Timeline {
+  private static final class InfinitelyLoopingTimeline extends ForwardingTimeline {
 
-    private final Timeline childTimeline;
+    public InfinitelyLoopingTimeline(Timeline timeline) {
-
+      super(timeline);
-    public InfinitelyLoopingTimeline(Timeline childTimeline) {
-      this.childTimeline = childTimeline;
-    }
-
-    @Override
-    public int getWindowCount() {
-      return childTimeline.getWindowCount();
     }
 
     @Override
     public int getNextWindowIndex(int windowIndex, @Player.RepeatMode int repeatMode) {
-      int childNextWindowIndex = childTimeline.getNextWindowIndex(windowIndex, repeatMode);
+      int childNextWindowIndex = timeline.getNextWindowIndex(windowIndex, repeatMode);
       return childNextWindowIndex == C.INDEX_UNSET ? 0 : childNextWindowIndex;
     }
 
     @Override
     public int getPreviousWindowIndex(int windowIndex, @Player.RepeatMode int repeatMode) {
-      int childPreviousWindowIndex = childTimeline.getPreviousWindowIndex(windowIndex, repeatMode);
+      int childPreviousWindowIndex = timeline.getPreviousWindowIndex(windowIndex, repeatMode);
       return childPreviousWindowIndex == C.INDEX_UNSET ? getWindowCount() - 1
           : childPreviousWindowIndex;
     }
 
-    @Override
-    public Window getWindow(int windowIndex, Window window, boolean setIds,
-        long defaultPositionProjectionUs) {
-      return childTimeline.getWindow(windowIndex, window, setIds, defaultPositionProjectionUs);
-    }
-
-    @Override
-    public int getPeriodCount() {
-      return childTimeline.getPeriodCount();
-    }
-
-    @Override
-    public Period getPeriod(int periodIndex, Period period, boolean setIds) {
-      return childTimeline.getPeriod(periodIndex, period, setIds);
-    }
-
-    @Override
-    public int getIndexOfPeriod(Object uid) {
-      return childTimeline.getIndexOfPeriod(uid);
-    }
-
   }
 
 }