Refactor to convert four state booleans to int.

Replace four booleans (mDrawPending, mCommitDrawPending, mReadyToShow
and mHasDrawn) with a single int that can take on the four states.

Move mLastHidden from WindowState to WindowStateAnimator.

Change-Id: Ieff319dfa19123bf5a6cdc98e9ab28fd432b8153