Clear gapless playback metadata for clipped media

Also pass an unresolved end point to ClippingMediaPeriod. This removes some
assertions checking timestamps in the ClippingMediaPeriod, but makes it
possible to identify when the end point is at the end of the media.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=167683358

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

@@ -270,7 +270,14 @@ public final class ClippingMediaPeriod implements MediaPeriod, MediaPeriod.Callb
         return C.RESULT_BUFFER_READ;
       }
       int result = stream.readData(formatHolder, buffer, requireFormat);
-      // TODO: Clear gapless playback metadata if a format was read (if applicable).
+      if (result == C.RESULT_FORMAT_READ) {
+        // Clear gapless playback metadata if the start/end points don't match the media.
+        Format format = formatHolder.format;
+        int encoderDelay = startUs != 0 ? 0 : format.encoderDelay;
+        int encoderPadding = endUs != C.TIME_END_OF_SOURCE ? 0 : format.encoderPadding;
+        formatHolder.format = format.copyWithGaplessInfo(encoderDelay, encoderPadding);
+        return C.RESULT_FORMAT_READ;
+      }
       if (endUs != C.TIME_END_OF_SOURCE && ((result == C.RESULT_BUFFER_READ
           && buffer.timeUs >= endUs) || (result == C.RESULT_NOTHING_READ
           && mediaPeriod.getBufferedPositionUs() == C.TIME_END_OF_SOURCE))) {

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

@@ -98,7 +98,7 @@ public final class ClippingMediaSource implements MediaSource, MediaSource.Liste
     ClippingMediaPeriod mediaPeriod = new ClippingMediaPeriod(
         mediaSource.createPeriod(id, allocator), enableInitialDiscontinuity);
     mediaPeriods.add(mediaPeriod);
-    mediaPeriod.setClipping(clippingTimeline.startUs, clippingTimeline.endUs);
+    mediaPeriod.setClipping(startUs, endUs);
     return mediaPeriod;
   }
 
@@ -119,9 +119,6 @@ public final class ClippingMediaSource implements MediaSource, MediaSource.Liste
   public void onSourceInfoRefreshed(Timeline timeline, Object manifest) {
     clippingTimeline = new ClippingTimeline(timeline, startUs, endUs);
     sourceListener.onSourceInfoRefreshed(clippingTimeline, manifest);
-    long startUs = clippingTimeline.startUs;
-    long endUs = clippingTimeline.endUs == C.TIME_UNSET ? C.TIME_END_OF_SOURCE
-        : clippingTimeline.endUs;
     int count = mediaPeriods.size();
     for (int i = 0; i < count; i++) {
       mediaPeriods.get(i).setClipping(startUs, endUs);