Fix up 'clear recents' UX.

Use the 'dismiss all' button drawable and place the button in the upper
right corner. Doing so fixes the broken animation when going into
recents.

Change-Id: I497a8b023f1872c5f9ae5df87af6ed2159e6b7b1
(cherry picked from commit 2283e0a29f57bb537ab82480c37dd4ce482a61f3)