Add UTF8 Check to text track serialization

Bug: 1316963
Change-Id: I18cf36dfe925c2cae332330d2eb21cedffacc5ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3611234
Reviewed-by: Frank Liberato <liberato@chromium.org>
Commit-Queue: Ted (Chromium) Meyer <tmathmeyer@chromium.org>
Auto-Submit: Ted (Chromium) Meyer <tmathmeyer@chromium.org>
Cr-Commit-Position: refs/heads/main@{#997350}

media/base/media_serializers.h

@@ -360,8 +360,10 @@ struct MediaSerializer<TextTrackConfig> {
     base::Value result(base::Value::Type::DICTIONARY);
     FIELD_SERIALIZE("kind", value.kind());
     FIELD_SERIALIZE("language", value.language());
-    if (value.label().length())
+    if (value.label().length() &&
+        base::IsStringUTF8AllowingNoncharacters(value.label())) {
       FIELD_SERIALIZE("label", value.label());
+    }
     return result;
   }
 };