Flush the animation if it is canceled

The issue was that: if navigation bar is requested to show while a
controller is playing an animation of hiding both status bar and
navigation bar, the animation will be canceled and will stay in an
intermediate state, and then, another controller will play an animation
of showing navigation bar. At the end, status bar will stay visible but
it should be invisible.

This CL fast-forwards the insets animation to the end state if it is
canceled.

Fix: 185459811
Test: Steps in the bug.
Change-Id: Id6ae321b6c153ed1d7155afd6111b193ac9c045c