Retain current visibility when copying layoutparam

The LayoutParams members, systemUiVisibility and
subtreeSystemUiVisibility are derived values rather than app-generated
values. When copying LayoutParams members make sure these values are
not overwritten.

Overwriting them was causing the STATUS_BAR_DISABLE_XXX flags to be
overwritten exposing elements that should have remained hidden.

Fixes bug b6374541.

Change-Id: Iaae4b4167e1b148bbdba4d05f473844f7fa3bf8d