function setUserAgentData(userAgentData) {
  userAgentDataInternal = userAgentData;
}
Override the user agent data object with the given value.
This should only be used for testing within the goog.labs.userAgent
namespace.
Pass `null` to specify the absence of userAgentData. Note that this behavior
is different from setUserAgent.
@param {?NavigatorUAData} userAgentData The userAgentData override.