Support handling metadata queries for MetadataRetriever.

- Support handling metadata queries (a.k.a get TrackGroupArray, which contains
Format and associated Metadata) from MetadataRetriever.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=195401204

constants.gradle

@@ -31,6 +31,7 @@ project.ext {
     junitVersion = '4.12'
     truthVersion = '0.39'
     robolectricVersion = '3.7.1'
+    autoValueVersion = '1.6'
     checkerframeworkVersion = '2.5.0'
     modulePrefix = ':'
     if (gradle.ext.has('exoplayerModulePrefix')) {

library/core/build.gradle

@@ -55,6 +55,8 @@ dependencies {
     testImplementation 'junit:junit:' + junitVersion
     testImplementation 'org.mockito:mockito-core:' + mockitoVersion
     testImplementation 'org.robolectric:robolectric:' + robolectricVersion
+    testImplementation 'com.google.auto.value:auto-value-annotations:' + autoValueVersion
+    testAnnotationProcessor 'com.google.auto.value:auto-value:' + autoValueVersion
 }
 
 ext {