Make IME fit navgation bars at left and right sides

IME is not big enough to be the background of navigation bar when
navigation bar is on the left or right edge of the screen. Also,
IME can be on top of navigation bar in landscape split-screen mode,
we don't want IME to block touches on navigation bar.

Fix: 151083985
Test: 1. Open Messages.
      2. Rotate device to landscape.
      3. Click on "Search message" and see if IME extends into
         the navigation bar area at the left or right edge.
Change-Id: I0ef3d6379a9ae52b3749154d2fdc54e9aa94a9e0