Fix restore of view and text wrap scales.

Fixes bug 5507881: Open pages in overview doesn't stick on initial
browser load.

Update the fix for bug 5230909: Zoom not restored on Back.

Added a boolean to indicate that scales have been restored. In the case
of restored scales (view and text wrap) being zero, set them to overview
and reading level respectively.

Change-Id: I5a22dd2040a22ee3b48c5903b586a65a4fa320f2