Don't select more than one audio/video/text track by default

Issue: #2618

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=156986606

library/core/src/main/java/com/google/android/exoplayer2/trackselection/DefaultTrackSelector.java

@@ -436,35 +436,48 @@ public class DefaultTrackSelector extends MappingTrackSelector {
     int rendererCount = rendererCapabilities.length;
     TrackSelection[] rendererTrackSelections = new TrackSelection[rendererCount];
     Parameters params = paramsReference.get();
-    boolean videoTrackAndRendererPresent = false;
 
+    boolean seenVideoRendererWithMappedTracks = false;
+    boolean selectedVideoTracks = false;
     for (int i = 0; i < rendererCount; i++) {
       if (C.TRACK_TYPE_VIDEO == rendererCapabilities[i].getTrackType()) {
+        if (!selectedVideoTracks) {
           rendererTrackSelections[i] = selectVideoTrack(rendererCapabilities[i],
               rendererTrackGroupArrays[i], rendererFormatSupports[i], params.maxVideoWidth,
               params.maxVideoHeight, params.maxVideoBitrate, params.allowNonSeamlessAdaptiveness,
               params.allowMixedMimeAdaptiveness, params.viewportWidth, params.viewportHeight,
               params.orientationMayChange, adaptiveTrackSelectionFactory,
-            params.exceedVideoConstraintsIfNecessary, params.exceedRendererCapabilitiesIfNecessary);
-        videoTrackAndRendererPresent |= rendererTrackGroupArrays[i].length > 0;
+              params.exceedVideoConstraintsIfNecessary,
+              params.exceedRendererCapabilitiesIfNecessary);
+          selectedVideoTracks = rendererTrackSelections[i] != null;
+        }
+        seenVideoRendererWithMappedTracks |= rendererTrackGroupArrays[i].length > 0;
       }
     }
 
+    boolean selectedAudioTracks = false;
+    boolean selectedTextTracks = false;
     for (int i = 0; i < rendererCount; i++) {
       switch (rendererCapabilities[i].getTrackType()) {
         case C.TRACK_TYPE_VIDEO:
           // Already done. Do nothing.
           break;
         case C.TRACK_TYPE_AUDIO:
+          if (!selectedAudioTracks) {
             rendererTrackSelections[i] = selectAudioTrack(rendererTrackGroupArrays[i],
                 rendererFormatSupports[i], params.preferredAudioLanguage,
                 params.exceedRendererCapabilitiesIfNecessary, params.allowMixedMimeAdaptiveness,
-              videoTrackAndRendererPresent ? null : adaptiveTrackSelectionFactory);
+                seenVideoRendererWithMappedTracks ? null : adaptiveTrackSelectionFactory);
+            selectedAudioTracks = rendererTrackSelections[i] != null;
+          }
           break;
         case C.TRACK_TYPE_TEXT:
+          if (!selectedTextTracks) {
             rendererTrackSelections[i] = selectTextTrack(rendererTrackGroupArrays[i],
                 rendererFormatSupports[i], params.preferredTextLanguage,
                 params.preferredAudioLanguage, params.exceedRendererCapabilitiesIfNecessary);
+            selectedTextTracks = rendererTrackSelections[i] != null;
+          }
           break;
         default:
           rendererTrackSelections[i] = selectOtherTrack(rendererCapabilities[i].getTrackType(),