Set initial view scale to be at least overview scale.

Some website will have an initial view scale which is less
than the overview scale and the page will display poorly.

This fix sets the initial scale and text wrap scale to be at least
overview scale to make the page looking good at first load.  When a page
is restored, the scale will not be changed.

Also make the reading level scale always bigger than overview
scale for consistency.

issue: 3226625
Change-Id: I8b77cf4fda454a35c3037fa09aaff1aac0c0f664