private void setScrollState(int newState) {
        if (mScrollState == newState) {
            return;
        }

        mScrollState = newState;
        if (mPageTransformer != null) {
            // PageTransformers can do complex things that benefit from hardware layers.
            enableLayers(newState != SCROLL_STATE_IDLE);
        }
        for (OnPageChangeListener eachListener : mOnPageChangeListeners) {
            if (eachListener != null) {
                eachListener.onPageScrollStateChanged(newState);
            }
        }
    }
Used internally to tag special types of child views that should be added as
pager decorations by default.
library/src/main/java/com/daimajia/slider/library/Tricks/ViewPagerEx.java