New navigation bar dimensions api

Get the short side of navigation bar dimensions

getNavigationBarWidth() returns width when navbar is vertical
on the screen

getNavigationBarHeight() returns height when navbar is horizontal
on the screen

public int getNavigationBarWidth();
public int getNavigationBarHeight();

Both return 0 if no bar is currently visible

If we need the long side dimensions, we can call WindowManager
and get screen dimensions as the navbar long side takes the full
long side of the screen

Change-Id: Idc3ca804fc9da95515b214b96b7d5800cd0b0631