static isParentOf(possibleParent, possibleChild) {
    const LanguageUtils = shaka.util.LanguageUtils;

    // Even through they SHOULD already be normalized, let's just be safe and
    // do it again.
    possibleParent = LanguageUtils.normalize(possibleParent);
    possibleChild = LanguageUtils.normalize(possibleChild);

    // Get all components. This should only be language and region
    // since we do not support dialect.
    /** @type {!Array<string>} */
    const possibleParentComponents =
        LanguageUtils.disassembleLocale_(possibleParent);
    /** @type {!Array<string>} */
    const possibleChildComponents =
        LanguageUtils.disassembleLocale_(possibleChild);

    return possibleParentComponents[0] == possibleChildComponents[0] &&
           possibleParentComponents.length == 1 &&
           possibleChildComponents.length == 2;
  }
Check if |possibleParent| is the parent locale of |possibleChild|. Because
we do not support dialects, the parent-child relationship is a lot simpler.
In a parent child relationship:
   - The parent and child have the same language-component
   - The parent has no region-component
   - The child has a region-component

Example:
 Locale A | Locale B | Is A The parent of B?
 --------------------------------------------
 en-US    | en-US    | no
 en-US    | en       | no
 en       | en-US    | yes
 en       | en       | no
 en       | fr       | no

@param {string} possibleParent
@param {string} possibleChild
@return {boolean}
@export