Clamp initial scale between minimum and maximum values.

Fixes bug 5515454: web page is not optimized (gmarket)

Initial scale is used to detect mobile sites
In ICS, mobile site detection based on whether the URL included m.,
mobile., wap., etc. has been removed in exclusive favor of the meta
viewport tag.

Within meta viewport tag, mobile site detection uses width (set to
device-width), initial-scale (set to 1.0 or default scale), etc. Make
this logic more robust by clamping initial scale between minimum and
maximum values, if specified.

Change-Id: I663c50ce20b35279d37a8c812e91d6bc4c16c1d3