function isAtLeast(brand, majorVersion) {
  assert(
      Math.floor(majorVersion) === majorVersion,
      'Major version must be an integer');
  return versionOf_(brand) >= majorVersion;
}
Returns true if the current browser matches the given brand and is at least
the given major version. The major version must be a whole number (i.e.
decimals should not be used to represent a minor version).
@param {!AllBrandsInternal} brand The brand whose version should be returned.
@param {number} majorVersion The major version number to compare against.
    This must be a whole number.
@return {boolean} Whether the current browser both matches the given brand
    and is at least the given version.