Do not grow the viewport width to infinite to fit

the content. Limit the overview viewport width to
a level that if a site behaves badly, the WebView
still does reasonably.

Partially fix http://b/issue?id=2209659
maps.yahoo.com keeps growing due to a layout bug.
This prevents the browser to go insane.

Partially fix http://b/issue?id=2215387
caltrain.com has a super long   which caused
the page super wide. This prevents the browser to
become unusable.

This change will make sites like, caltrain.com/timetable.html
not fit all in the view. You have to scroll left
and right. And it is same as iPhone.