Use Timeline.getPeriodPosition to resolve period index in ExoPlayerImpl.seekTo

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=174460558

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

@@ -21,6 +21,7 @@ import android.os.Looper;
 import android.os.Message;
 import android.os.Message;
 import android.support.annotation.Nullable;
 import android.support.annotation.Nullable;
 import android.util.Log;
 import android.util.Log;
+import android.util.Pair;
 import com.google.android.exoplayer2.source.MediaSource;
 import com.google.android.exoplayer2.source.MediaSource;
 import com.google.android.exoplayer2.source.MediaSource.MediaPeriodId;
 import com.google.android.exoplayer2.source.MediaSource.MediaPeriodId;
 import com.google.android.exoplayer2.source.TrackGroupArray;
 import com.google.android.exoplayer2.source.TrackGroupArray;
@@ -254,19 +255,12 @@ import java.util.concurrent.CopyOnWriteArraySet;
       maskingWindowPositionMs = positionMs == C.TIME_UNSET ? 0 : positionMs;
       maskingWindowPositionMs = positionMs == C.TIME_UNSET ? 0 : positionMs;
       maskingPeriodIndex = 0;
       maskingPeriodIndex = 0;
     } else {
     } else {
-      timeline.getWindow(windowIndex, window);
-      long windowPositionUs = positionMs == C.TIME_UNSET ? window.getDefaultPositionUs()
-          : C.msToUs(positionMs);
-      int periodIndex = window.firstPeriodIndex;
-      long periodPositionUs = window.getPositionInFirstPeriodUs() + windowPositionUs;
-      long periodDurationUs = timeline.getPeriod(periodIndex, period).getDurationUs();
-      while (periodDurationUs != C.TIME_UNSET && periodPositionUs >= periodDurationUs
-          && periodIndex < window.lastPeriodIndex) {
-        periodPositionUs -= periodDurationUs;
-        periodDurationUs = timeline.getPeriod(++periodIndex, period).getDurationUs();
-      }
+      long windowPositionUs = positionMs == C.TIME_UNSET
+          ? timeline.getWindow(windowIndex, window).getDefaultPositionUs() : C.msToUs(positionMs);
+      Pair<Integer, Long> periodIndexAndPositon =
+          timeline.getPeriodPosition(window, period, windowIndex, windowPositionUs);
       maskingWindowPositionMs = C.usToMs(windowPositionUs);
       maskingWindowPositionMs = C.usToMs(windowPositionUs);
-      maskingPeriodIndex = periodIndex;
+      maskingPeriodIndex = periodIndexAndPositon.first;
     }
     }
     internalPlayer.seekTo(timeline, windowIndex, C.msToUs(positionMs));
     internalPlayer.seekTo(timeline, windowIndex, C.msToUs(positionMs));
     for (Player.EventListener listener : listeners) {
     for (Player.EventListener listener : listeners) {