SurfaceView: Don't destroy Surface while Stopped.

We instead just want to leave it floating, and let
it's lifetime be controlled by the parent surface. This way it can
take part in animations. Normally the WindowManager handles this by
calling detachChildren but it seems sometimes stop arrives before
the window manager is even clued in. Rather than bringing ActivityManager
in to the detach children dance...this seemed more appropriate and very similar
to the behavior before SV->SurfaceControl port.

Bug: 37922210
Test: Manual from bug + Launch chrome a bunch
Change-Id: Iee4fb0078a6e8dfd4c7acdb0107f8edd3a995634