Always using middle position to resize layout

After rotation, the divider should always in middle if not in
minimized mode, so it should use middle position rather than
divider current position to resize split on rotation callback.

Fix: 192219057
Test: manual
Test: atest WMShellUnitTests
Change-Id: I255c1d6aad9a796ca3ec722f45977eb360fe3805
1 file changed