Revert discarding empty ad breaks

The previous change was too aggressive as it would clear future ad breaks.

Still clear the pending content position so the real content position is
reported after an empty ad break.

Issue: #4681
Issue: #4622

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=209752306

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

@@ -631,11 +631,8 @@ public VideoProgressUpdate getContentProgress() {
     } else if (fakeContentProgressElapsedRealtimeMs != C.TIME_UNSET) {
       long elapsedSinceEndMs = SystemClock.elapsedRealtime() - fakeContentProgressElapsedRealtimeMs;
       contentPositionMs = fakeContentProgressOffsetMs + elapsedSinceEndMs;
-      int adGroupIndexForPosition =
+      expectedAdGroupIndex =
           adPlaybackState.getAdGroupIndexForPositionUs(C.msToUs(contentPositionMs));
-      if (adGroupIndexForPosition != C.INDEX_UNSET) {
-        expectedAdGroupIndex = adGroupIndexForPosition;
-      }
     } else if (imaAdState == IMA_AD_STATE_NONE && !playingAd && hasContentDuration) {
       contentPositionMs = player.getCurrentPosition();
       // Update the expected ad group index for the current content position. The update is delayed
@@ -1127,15 +1124,6 @@ private void handleAdGroupLoadError(Exception error) {
     if (pendingAdLoadError == null) {
       pendingAdLoadError = AdLoadException.createForAdGroup(error, adGroupIndex);
     }
-    // Discard the ad break, which makes sure we don't receive duplicate load error events.
-    adsManager.discardAdBreak();
-    // Set the next expected ad group index so we can handle multiple load errors in a row.
-    adGroupIndex++;
-    if (adGroupIndex < adPlaybackState.adGroupCount) {
-      expectedAdGroupIndex = adGroupIndex;
-    } else {
-      expectedAdGroupIndex = C.INDEX_UNSET;
-    }
     pendingContentPositionMs = C.TIME_UNSET;
   }