Add constraint based track selection for ExoCast

PiperOrigin-RevId: 231764284

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

@@ -354,7 +354,7 @@ public class DefaultTrackSelector extends MappingTrackSelector {
     // Audio
 
     @Override
-    public ParametersBuilder setPreferredAudioLanguage(String preferredAudioLanguage) {
+    public ParametersBuilder setPreferredAudioLanguage(@Nullable String preferredAudioLanguage) {
       super.setPreferredAudioLanguage(preferredAudioLanguage);
       return this;
     }
@@ -415,7 +415,7 @@ public class DefaultTrackSelector extends MappingTrackSelector {
     // Text
 
     @Override
-    public ParametersBuilder setPreferredTextLanguage(String preferredTextLanguage) {
+    public ParametersBuilder setPreferredTextLanguage(@Nullable String preferredTextLanguage) {
       super.setPreferredTextLanguage(preferredTextLanguage);
       return this;
     }

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

@@ -63,7 +63,7 @@ public class TrackSelectionParameters implements Parcelable {
      *     639-2 three-letter code.
      * @return This builder.
      */
-    public Builder setPreferredAudioLanguage(String preferredAudioLanguage) {
+    public Builder setPreferredAudioLanguage(@Nullable String preferredAudioLanguage) {
       this.preferredAudioLanguage = preferredAudioLanguage;
       return this;
     }
@@ -77,7 +77,7 @@ public class TrackSelectionParameters implements Parcelable {
      *     three-letter code.
      * @return This builder.
      */
-    public Builder setPreferredTextLanguage(String preferredTextLanguage) {
+    public Builder setPreferredTextLanguage(@Nullable String preferredTextLanguage) {
       this.preferredTextLanguage = preferredTextLanguage;
       return this;
     }