Make system layout fill the window properly on expanded desktop mode.
This commit fixes e.g. the gap on the bottom of the lock screen or the gap on the right side of status bar on landscape mode.
Original CM commit has been modified to respect the customization of the navigation bar height, implemented here: https://github.com/rascarlo/platform_frameworks_base/commit/d60327dfeb1666a0d13ed2c7c3ceab18e466e6bd
Original CM commit use com.android.internal.R.dimen.navigation_bar_height/width to get the navigation bar default dimensions, I use mNavButtonsHeight * DisplayMetrics.DENSITY_DEVICE/DisplayMetrics.DENSITY_DEFAULT

Change-Id: Ic8a6b748f94d7dcc883201579d199898713c90fd