设置渐变色 StatusBar

用 SystemBarTintManager 实现很简单，就几行代码：

private void tintStatusBar(@NonNull Activity activity, @ColorInt int startColor, @ColorInt int endColor) {
    Window window = activity.getWindow();
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
      window.clearFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
      window.addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
      window.setStatusBarColor(Color.TRANSPARENT);
    } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
      window.addFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS);
    }
    GradientDrawable drawable =
        new GradientDrawable(LEFT_RIGHT, new int[] { startColor, endColor });

    final SystemBarTintManager tintManager = new SystemBarTintManager(this);
    // enable status bar tint
    tintManager.setStatusBarTintEnabled(true);
    tintManager.setNavigationBarTintEnabled(false);
    tintManager.setTintDrawable(drawable);
  }