Add QoE field reporter for formats.

This reports video and audio format selections.
See [] for spec details.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=199627176

library/core/src/main/java/com/google/android/exoplayer2/util/MimeTypes.java

@@ -278,7 +278,7 @@ public final class MimeTypes {
    * @param mimeType The MIME type.
    * @param mimeType The MIME type.
    * @return The {@link C}{@code .TRACK_TYPE_*} constant that corresponds to a specified MIME type.
    * @return The {@link C}{@code .TRACK_TYPE_*} constant that corresponds to a specified MIME type.
    */
    */
-  public static int getTrackType(String mimeType) {
+  public static int getTrackType(@Nullable String mimeType) {
     if (TextUtils.isEmpty(mimeType)) {
     if (TextUtils.isEmpty(mimeType)) {
       return C.TRACK_TYPE_UNKNOWN;
       return C.TRACK_TYPE_UNKNOWN;
     } else if (isAudio(mimeType)) {
     } else if (isAudio(mimeType)) {