Cherry-pick: [Android WebView] Fixed width set in the viewport tag must not be scaled by target-densitydpi

Cherry-pick of chromium http://crrev.com/25356004

Bug: 10894860

Original description:

Legacy WebView only scales the layout width if it is set to 'device-width' or 'auto',
but not if it is set explicitly as a numeric value.

BUG=302974

Change-Id: Ia5e031a9d64188a8390accad53c76c23e519254c
3 files changed