Preserve activity & web view state across rotation etc

We spent a bunch of trouble looking into ways to preserve the scroll
position and other state across orientation changes, with mediocre
results.

Turns out the Browser app simply ensures that it preserves the activity
across orientation and screen size changes -- the webView naturally
keeps the correct scroll position across an orientation change if we
just let it be instead of recreating everything.

Note we may still need to preserve scroll position explicitly across
an activity being killed or something, so haven't removed that existing
code using the basic scrollY position.

Bug: 61512
Change-Id: Iec3ae929d1bd8b0af2d94dcb9664827d659a235d