Fix issue #5384631: hw windows not resizing correctly

When the SystemUi becomes visible, the activity window resizes.
The hardware renderer was not begin resized to suit, so it was drawing
to a surface larger than that of the activity window, and some of the
rendering (like the action bar) appeared off the screen.

The fix is to keep track of the surface size in HardwareRenderer and to
recreate the surface when the size changes.

This change also removes the BUFFER_CHANGE flag from WindowManager.LayoutParams.
The only reason the flag existed was to trigger a hardware surface recreation,
but checking the old/new size is a more direct way of handling this.

Change-Id: I9d6bf6385794886d1d93c60609c170864cdcdfab