更新$referrer 为什么会有400毫秒的限制呢？

[hlz217057]

public static void setCurrentTitle(String currentScreenTitle) {
if (System.currentTimeMillis() - sReferrerTitleTime >= 400) {// update referrer
mReferrerTitle = mCurrentTitle;
sReferrerTitleTime = System.currentTimeMillis();
}
mCurrentTitle = currentScreenTitle;
}