Framework定制系列（一）-----SystemUI NavigationBar导航栏上滑返回Launcher

代码路径：frameworks/base/services/core/java/com/android/server/wm/DisplayPolicy.java
注：SystemUI Navigationbar非隐藏状态可上滑，如有隐藏导航栏需求，height设置为1dp。

@Override
public void onSwipeFromBottom() {
	if (mNavigationBar != null && mNavigationBarPosition == NAV_BAR_BOTTOM) {
		// Log.d("ljx", "=========onSwipeFromBottom=========");
		// 导航栏上滑相关功能需求代码写这里。
		requestTransientBars(mNavigationBar);
	}
}

代码路径：frameworks/base/services/core/java/com/android/server/wm/DisplayPolicy.java

@Override
public void onSwipeFromBottom() {
	if (mNavigationBar != null && mNavigationBarPosition == NAV_BAR_BOTTOM) {
+		/**add by ljx@date for re